Front-end exploration tour

Introduction:

"Front-end Exploration Journey" is a simple-to-depth front-end development guide, designed to help readers start from scratch and gradually master the core knowledge and skills of front-end development. Combined with actual project cases, this book explains various concepts and technologies in front-end development with easy-to-understand language and rich illustrations, and provides practical programming examples and exercises.

Content outline:

Part 1: Getting Started with the Basics

• Chapter 1: Introduction to Front-End Development
• Chapter 2: HTML Basics
• Chapter 3: CSS Basics
• Chapter 4: JavaScript Basics

Part II: Front-end frameworks and tools

• Chapter 5: Overview of Front-End Frameworks
• Chapter 6: Getting started with React
• Chapter 7: Getting started with Vue
• Chapter 8: Getting started with Angular
• Chapter 9: Introduction to commonly used front-end tools

Part III: Front-end performance optimization and debugging

• Chapter 10: Principles of Front-End Performance Optimization
• Chapter 11: Page Load Optimization
• Chapter 12: Front-end debugging techniques and tools

Part IV: Front-End Security and Cross-Platform Development

• Chapter 13: Front-End Security Overview
• Chapter 14: Front-End Security Practices
• Chapter 15: Getting Started with Cross-Platform Development

Part V: Advanced Front-End and Best Practices

• Chapter 16: Front-End Engineering and Modularization
• Chapter 17: Front-End Design Patterns and Best Practices
• Chapter 18: Front-end automated testing

appendix:

• Appendix A: Common front-end resources and recommended learning materials
• Appendix B: Analysis of common front-end interview questions

Features and Highlights:

1. Incremental learning: This book divides the knowledge points of front-end development according to the degree of difficulty, so that readers can master the skills step by step.

2. Practical case guidance: Each chapter provides practical project cases, and guides readers to practice through programming examples and exercises, so as to deepen the understanding of concepts and application ability.

3. Comprehensive introduction to mainstream frameworks: In addition to introducing the basics of HTML, CSS and JavaScript, it also provides an in-depth explanation of the basic usage and principles of mainstream front-end frameworks such as React, Vue and Angular.

4. Pay attention to performance optimization and security: This book focuses on front-end performance optimization and security issues, and guides readers to avoid common performance and security risks in actual development.

5. Advanced front-end and best practices: By introducing advanced topics such as front-end engineering, design patterns, and automated testing, it helps readers become professionals with advanced front-end development capabilities.

Whether the reader is a beginner or a developer with a certain front-end foundation, they can gain valuable knowledge and experience through "Front-end Exploration Journey" and become an excellent front-end developer.

Chapter 1 Introduction to Front-End Development

In today's digital age, front-end development has become an important part of building Internet applications. Front-end development involves designing, coding, and optimizing the user interface, and is also responsible for interacting with back-end services to achieve data transfer and display.

This chapter guides readers through the basic concepts, job responsibilities, and required skills of front-end development. We will delve into the importance of front-end development, as well as the role and development prospects of front-end developers in different industries.

1.1 Definition and role of front-end development

Front-end development refers to the process of building and maintaining user interfaces, which includes using technologies such as HTML, CSS, and JavaScript to design and develop responsive, beautiful, and easy-to-use web pages and applications. Front-end development acts as a bridge, connecting users with the back-end services of Internet applications, enabling users to interact directly with the application.

1.2 Responsibilities of front-end development

The responsibilities of front-end developers usually include the following aspects:

• Create user interfaces for web pages and applications using technologies such as HTML, CSS, and JavaScript.
• Work with the design team to translate designs into interactive user interfaces.
• Work closely with back-end developers to realize data delivery and display.
• Optimize the performance of the user interface and improve the user experience.
• Cross-browser and cross-device testing ensures app compatibility on different platforms.
• Learn and familiarize yourself with new technologies and tools to continuously improve your skills.

1.3 Skill requirements for front-end development

Becoming a good front-end developer requires the following skills:

• Master the basics of HTML, CSS, and JavaScript, and learn about their latest standards and specifications.
• Familiar with mainstream front-end frameworks such as React, Vue and Angular, and understand their usage and principles.
• Proficient in responsive layout and mobile terminal development techniques to meet the needs of different devices.
• Familiar with various debugging tools and techniques, able to quickly locate and solve problems.
• Good communication and teamwork skills, able to work closely with designers and backend developers.

1.4 Development prospect of front-end development

With the vigorous development of the Internet, the demand for front-end development is also increasing. Front-end developers have a wide range of employment opportunities in a variety of industries, including software development companies, Internet companies, media and advertising companies, and more. At the same time, with the popularity of mobile applications and the continuous emergence of new technologies, the development prospects of front-end development are even broader.

Summarize:

In this chapter, we introduce the basic concepts, responsibilities and skill requirements of front-end development, and look forward to the development prospects of front-end development. In the following chapters, we will deeply explore the core technologies of front-end development such as HTML, CSS, and JavaScript, and help readers gradually master the basic knowledge and skills of front-end development through practical examples. I hope readers can find inspiration and guidance in this book and become an excellent front-end developer.

Chapter 2 HTML Basics

HTML (HyperText Markup Language) is a markup language used to build web page structures. In this chapter, we will discuss in depth the basic syntax of HTML, common tags and elements, and how to use them to create web pages.

2.1 Basic structure of HTML

A basic HTML document consists of <!DOCTYPE>, , and elements. Here is an example:

<!DOCTYPE html>
<html>
<head>
    <title>我的网页</title>
</head>
<body>
    <h1>欢迎来到我的网页</h1>
    <p>这是一个简单的示例网页。</p>
</body>
</html>

• : This is the tag that declares the document type, which tells the browser to use HTML5 to parse the web page.
• : The root element of the entire HTML document, including child elements such as and .
• : Metadata used to define web pages, such as titles, style sheets, and scripts.
• : Contains the actual content of the web page, such as titles, paragraphs, pictures, and links.

2.2 Common HTML tags and elements

HTML provides a series of tags and elements used to define the structure and content of web pages. Here are some examples of common HTML tags and elements:

• title:

  to

<h1>这是一级标题</h1>
<h2>这是二级标题</h2>

• paragraph:

<p>这是一个段落。</p>

• image:

<img src="image.jpg"/>

Chapter 3 CSS Basics

CSS (Cascading Style Sheets) is a language for styling web pages. In this chapter, we will introduce the basic syntax, selectors, and common properties of CSS, and how to use them to beautify the appearance and layout of web pages.

3.1 Basic syntax of CSS

CSS consists of a series of rules, and each rule consists of a selector and a declaration block. Here is a simple example:

h1 {
    
    
    color: blue;
    font-size: 24px;
}

• Selector: Used to select the HTML element to apply the style to. h1For example, the selector in the example above applies the style to all <h1>elements.
• Declaration block: {}Wrapped by a pair of curly braces, it contains one or more attribute declarations. Each attribute declaration consists of an attribute name and an attribute value, :separated by a colon.

3.2 Common CSS selectors

CSS selectors are used to select specific HTML elements and apply corresponding styles. Here are some examples of common CSS selectors:

• Element selector: selects HTML elements of the specified type.

p {
    
    
    color: red;
}

• Class selector: selects HTML elements with the specified class name.

.my-class {
    
    
    font-size: 16px;
}

• ID Selector: Selects HTML elements with the specified ID.

#my-id {
    
    
    background-color: yellow;
}

• Descendant selector: Selects descendant elements of the specified element.

div p {
    
    
    font-weight: bold;
}

• Pseudo-class selector: special state of the selected element (such as hovering, visited, etc.).

a:hover {
    
    
    color: purple;
}

3.3 Common CSS properties

CSS provides a series of properties for controlling the appearance and layout of web page elements. Here are some examples of common CSS properties:

• color: Controls the text color.

h1 {
    
    
    color: blue;
}

• background-color: Controls the background color.

body {
    
    
    background-color: lightgray;
}

• font-size: Controls the font size.

p {
    
    
    font-size: 18px;
}

• margin: controls the outer margin.

div {
    
    
    margin-top: 10px;
    margin-bottom: 20px;
}

• padding: Control the inner margin.

h1 {
    
    
    padding-left: 20px;
    padding-right: 20px;
}

Summarize:

This chapter introduces the basic syntax, selectors, and common properties of CSS. By using CSS, we can add styles to HTML elements and beautify the appearance and layout of web pages. In the next chapters, we will delve into more advanced CSS techniques and layout methods to help readers create more attractive and interactive web pages. I hope readers can become skilled front-end developers by learning CSS.

Chapter 4 JavaScript Basics

JavaScript is a scripting language used to achieve interactive and dynamic effects on web pages. In this chapter, we will introduce the basic syntax, data types, variables and functions of JavaScript, and how to use it in web pages.

4.1 JavaScript Basic Syntax

;JavaScript consists of a series of statements, each terminated by a semicolon . Here is a simple example:

var name = "John";
console.log("Hello, " + name + "!");

• Variables: Containers for storing and manipulating data. In the above example, nameit is a variable that stores the string "John".
• Console Output: Use console.log()a function to output information to the browser's console.

4.2 JavaScript data types

JavaScript supports a variety of data types, including strings, numbers, booleans, arrays, and objects, among others. The following are examples of some common data types:

• String: Used to represent text.

var name = "John";

• Numbers: used to represent numerical values.

var age = 25;

• Boolean: A logical value representing true or false.

var isStudent = true;

• Array: Used to store an ordered collection of multiple values.

var numbers = [1, 2, 3, 4, 5];

• Object: Used to store collections of multiple properties and methods.

var person = {
    
    
    name: "John",
    age: 25,
    isStudent: true
};

4.3 JavaScript variables and functions

Variables in JavaScript are used to store data, and functions are used to perform specific tasks. Here are some examples of common variables and functions:

• Variable declaration and assignment:

var name;
name = "John";

• Function declaration and call:

function sayHello(name) {
    
    
    console.log("Hello, " + name + "!");
}
sayHello("John");

• Anonymous functions and callback functions:

var myFunction = function() {
    
    
    console.log("This is an anonymous function.");
}
setTimeout(myFunction, 1000);

Summarize:

This chapter introduces the basic syntax, data types, variables and functions of JavaScript. Through JavaScript, we can add interactive and dynamic effects to web pages to make them richer and more vivid. In the next chapters, we will delve into the advanced concepts and techniques of JavaScript to help readers further improve their front-end development capabilities. I hope readers can write more flexible and powerful web applications by learning JavaScript.

Chapter 5 Overview of Front-End Frameworks

In this chapter, we will introduce the concepts and functions of front-end frameworks, as well as the characteristics and usage examples of some common front-end frameworks.

5.1 Introduction to front-end framework

A front-end framework is a tool or library used to simplify and speed up front-end development. They provide abstraction and encapsulation that make it easier for developers to build complex, interactive, and high-performance web applications.

5.2 Features and examples of common front-end frameworks

• React: React is a JavaScript library developed by Facebook for building user interfaces. It adopts a componentized development model, which makes it easy to build reusable and efficient UI components.

// 使用React创建一个简单的组件
class App extends React.Component {
    
    
    render() {
    
    
        return <h1>Hello, React!</h1>;
    }
}
ReactDOM.render(<App />, document.getElementById("root"));

• Angular: Angular is a complete front-end framework developed by Google. It uses the architectural pattern of MVVM (Model View ViewModel) and provides a large number of functions and tools, including data binding, routing, form validation, etc.

// 使用Angular创建一个简单的组件
@Component({
    
    
    selector: 'app-hello',
    template: '<h1>Hello, Angular!</h1>'
})
export class HelloComponent {
    
     }

• Vue: Vue is a lightweight JavaScript framework that is easy to learn and use. It adopts a progressive development model, which can selectively introduce functions and libraries according to the needs of the project.

// 使用Vue创建一个简单的组件
new Vue({
    
    
    el: '#app',
    template: '<h1>Hello, Vue!</h1>'
});

5.3 Advantages and usage scenarios of the front-end framework

Front-end frameworks have the following advantages:

• An efficient and reusable development model is provided to speed up the development process.
• It abstracts and encapsulates common functions, reducing the learning cost for developers.
• Provides responsive layout and interactive effects for different devices and browsers.

The front-end framework is suitable for various front-end development scenarios, including single-page applications (SPA), responsive web design, mobile application development, etc.

Summary:
This chapter introduces the concepts, features and usage examples of the front-end framework. Front-end frameworks can greatly improve front-end development efficiency and enable more complex, interactive, and performance-optimized web applications. In the next chapters, we will explore some common front-end frameworks and tools in depth, help readers choose the framework that suits their project needs, and understand how to use them to build excellent front-end applications. I hope readers can become skilled front-end developers by learning the front-end framework.

Chapter 6 Overview of Front-End Frameworks

In this chapter, we will further introduce the concepts, characteristics and usage examples of front-end frameworks, and provide code samples of some common frameworks.

6.1 Introduction to front-end framework

A front-end framework is a tool or library used to simplify and speed up front-end development. They provide a series of abstractions and encapsulations to help developers build complex, interactive and high-performance web applications more efficiently.

6.2 Features and examples of common front-end frameworks

• React: React is a JavaScript library developed by Facebook for building user interfaces. It adopts a componentized development model, which makes it easy to build reusable and efficient UI components.

// 使用React创建一个简单的组件
class App extends React.Component {
    
    
    render() {
    
    
        return <h1>Hello, React!</h1>;
    }
}
ReactDOM.render(<App />, document.getElementById("root"));

• Angular: Angular is a complete front-end framework developed by Google. It uses the MVC (Model View Controller) architectural pattern and provides a large number of functions and tools, including data binding, routing, form validation, etc.

// 使用Angular创建一个简单的组件
@Component({
    
    
    selector: 'app-hello',
    template: '<h1>Hello, Angular!</h1>'
})
export class HelloComponent {
    
     }

• Vue: Vue is a lightweight JavaScript framework that is easy to learn and use. It adopts a progressive development model, which can selectively introduce functions and libraries according to the needs of the project.

// 使用Vue创建一个简单的组件
new Vue({
    
    
    el: '#app',
    template: '<h1>Hello, Vue!</h1>'
});

6.3 Advantages and usage scenarios of the front-end framework

Front-end frameworks have the following advantages:

• Improve development efficiency: The front-end framework provides an efficient and reusable development model, which accelerates the development process.
• Simplify complexity: The front-end framework abstracts and encapsulates common functions, reducing the learning cost for developers.
• Responsive design: The front-end framework provides responsive layout and interactive effects that adapt to different devices and browsers.

The front-end framework is suitable for various front-end development scenarios, including single-page applications (SPA), responsive web design, mobile application development, etc.

Summary:
This chapter introduces the concepts, features and usage examples of the front-end framework. Front-end frameworks can greatly improve front-end development efficiency and enable more complex, interactive, and performance-optimized web applications. In the next chapters, we will explore some common front-end frameworks and tools in depth, help readers choose the framework that suits their project needs, and learn how to use them to build excellent front-end applications. I hope readers can become skilled front-end developers by learning the front-end framework.

Chapter 6 Getting Started with React

In this chapter, we will introduce the basic concepts, usage methods and core features of React, and provide some React code examples.

6.1 Introduction to React

React is a JavaScript library developed by Facebook for building user interfaces. It adopts a componentized development model, which makes it easy to build reusable and efficient UI components. React uses virtual DOM (Virtual DOM) to improve performance and supports a data management mechanism for one-way data flow.

6.2 Creating a React application

To use React, you need to build a basic React application first. Here are the steps to create a React app:

1. Install Node.js: First, make sure you have Node.js installed on your computer. It can be downloaded from the official website and installed.

2. Create a React application: On the command line, use the create-react-app command to create a new React application.

npx create-react-app my-app

3. Enter the application directory: Enter the directory of the created React application.

cd my-app

4. Start the development server: Run the start command in the command line, which will automatically open the browser and load the development environment of the React application.

npm start

5. Editing React components: Edit the code of React components in the App.js file in the src directory.

import React from 'react';

class App extends React.Component {
    
    
  render() {
    
    
    return (
      <div>
        <h1>Hello, React!</h1>
      </div>
    );
  }
}

export default App;

6. Render the React application: In the index.js file in the src directory, render the React component to the root node.

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';

ReactDOM.render(<App />, document.getElementById('root'));

7. View the result: Now, you can view your React application in the browser.

6.3 React component development

The core concept of React is component development. Components are the basic unit of building React applications, and can divide the UI into independent, reusable and testable parts.

Here is an example of a simple React component:

import React from 'react';

class MyComponent extends React.Component {
    
    
  render() {
    
    
    return (
      <div>
        <h2>{
    
    this.props.title}</h2>
        <p>{
    
    this.props.content}</p>
      </div>
    );
  }
}

export default MyComponent;

Example usage:

import React from 'react';
import MyComponent from './MyComponent';

class App extends React.Component {
    
    
  render() {
    
    
    return (
      <div>
        <h1>Hello, React!</h1>
        <MyComponent title="Component Title" content="Component Content" />
      </div>
    );
  }
}

export default App;

In the above example, we defined a React component called MyComponent and used it in the App component. Through the props attribute, we can pass data to child components.

Summarize:

This chapter introduces the concept, usage and core features of React. By creating a basic React application and using React components for UI development, you can start to become familiar with the React way of development. In the next chapters, we will delve into the advanced topics and best practices of React to help you make better use of React to build excellent front-end applications. I hope you can become an excellent React developer by learning React.

Chapter 7 Getting Started with Vue

In this chapter, we will introduce the basic concepts, usage methods and core features of Vue, and provide some Vue code examples.

7.1 Introduction to Vue

Vue is a lightweight JavaScript framework that is easy to learn and use. It adopts a progressive development model, which can selectively introduce functions and libraries according to the needs of the project. The core of Vue is a JavaScript library for building user interfaces, which makes it easy to build interactive web applications through intuitive template syntax and declarative rendering.

7.2 Create a Vue application

To use Vue, you need to build a basic Vue application first. Here are the steps to create a Vue application:

1. Import the Vue library: import the Vue library in the HTML file.

<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>

2. Create a Vue instance: Create a Vue instance in a JavaScript file.

new Vue({
    
    
  el: '#app',
  data: {
    
    
    message: 'Hello, Vue!'
  }
});

3. Write HTML template: Define the HTML template bound to the Vue instance in the HTML file.

<div id="app">
  <h1>{
   
   { message }}</h1>
</div>

4. View the result: Now, you can view your Vue application in the browser.

7.3 Vue component development

The core concept of Vue is component development. Components are the basic unit of building Vue applications, dividing the UI into independent, reusable and testable parts.

Here is an example of a simple Vue component:

<template>
  <div>
    <h2>{
   
   { title }}</h2>
    <p>{
   
   { content }}</p>
  </div>
</template>

<script>
export default {
      
      
  name: 'MyComponent',
  data() {
      
      
    return {
      
      
      title: 'Component Title',
      content: 'Component Content'
    };
  }
}
</script>

Example usage:

<template>
  <div>
    <h1>Hello, Vue!</h1>
    <my-component></my-component>
  </div>
</template>

<script>
import MyComponent from './MyComponent.vue';

export default {
      
      
  components: {
      
      
    MyComponent
  }
}
</script>

In the above example, we defined a Vue component called MyComponent and used it in the App component. Through data attributes, we can pass data to child components.

Summary:
This chapter introduces the concept, usage and core features of Vue. By creating a basic Vue application and using Vue components for UI development, you can start to familiarize yourself with the Vue development method. In the next chapters, we will delve into the advanced topics and best practices of Vue to help you make better use of Vue to build excellent front-end applications. I hope you can become an excellent Vue developer by learning Vue.

Chapter 8 Getting Started with Angular

In this chapter, we will introduce the basic concepts, usage methods and core features of Angular, and provide some Angular code examples.

8.1 Introduction to Angular

Angular is a complete front-end framework developed by Google. It uses the MVC (Model View Controller) architectural pattern and provides a large number of functions and tools, including data binding, routing, form validation, etc. At the heart of Angular is a TypeScript library for building web applications.

8.2 Creating an Angular application

Using Angular requires building a basic Angular application first. Following are the steps to create an Angular application:

1. Install Angular CLI: First, make sure you have Node.js installed on your computer. Then, run the following command on the command line to install Angular CLI.

npm install -g @angular/cli

2. Create a new project: From the command line, use the Angular CLI to create a new Angular project.

ng new my-app

3. Go to project directory: Go to the directory of the created Angular project.

cd my-app

4. Start the development server: Run the start command on the command line, which will automatically start the development server and load your Angular application in the browser.

ng serve --open

5. Editing Components: Edit the code of Angular components in the component files in the src/app directory.

import {
    
     Component } from '@angular/core';

@Component({
    
    
  selector: 'app-hello',
  template: `
    <h1>Hello, Angular!</h1>
  `
})
export class HelloComponent {
    
     }

6. Using components: Import and declare Angular components as part of this module in the root component file in the src/app directory.

import {
    
     NgModule } from '@angular/core';
import {
    
     BrowserModule } from '@angular/platform-browser';
import {
    
     HelloComponent } from './hello.component';

@NgModule({
    
    
  declarations: [
    HelloComponent
  ],
  imports: [
    BrowserModule
  ],
  bootstrap: [HelloComponent]
})
export class AppModule {
    
     }

7. View the result: Now, you can view your Angular application in the browser.

8.3 Angular component development

The core concept of Angular is component development. Components are the basic unit of building Angular applications, dividing the UI into independent, reusable and testable parts.

Here is an example of a simple Angular component:

import {
    
     Component } from '@angular/core';

@Component({
    
    
  selector: 'app-my-component',
  template: `
    <div>
      <h2>{
     
     { title }}</h2>
      <p>{
     
     { content }}</p>
    </div>
  `
})
export class MyComponent {
    
    
  title = 'Component Title';
  content = 'Component Content';
}

Example usage:

import {
    
     Component } from '@angular/core';

@Component({
    
    
  selector: 'app-root',
  template: `
    <div>
      <h1>Hello, Angular!</h1>
      <app-my-component></app-my-component>
    </div>
  `
})
export class AppComponent {
    
     }

In the above example, we defined an Angular component called MyComponent and used it in the App component. With property binding, we can pass data to child components.

Summarize:

This chapter introduces the concept, usage and core features of Angular. By creating a basic Angular application and using Angular components for UI development, you can start to familiarize yourself with the Angular way of development. In the next chapters, we will delve into more advanced topics and best practices about Angular to help you make better use of Angular to build excellent front-end applications. I hope you can become an excellent Angular developer by learning Angular.

Chapter 9 Introduction to commonly used front-end tools

In this chapter, we will introduce some commonly used front-end tools and provide some code examples using these tools.

9.1 Package management tool: npm

npm (Node Package Manager) is the default package management tool for Node.js and one of the most commonly used package management tools in front-end development. It can help us download and manage various libraries and tools that the project depends on.

The following is an example of installing a dependent library using npm:

npm install axios

9.2 Module packaging tool: webpack

webpack is a module packaging tool that packages multiple modules into one or more bundle files. It can handle various resources such as JavaScript, CSS, images, etc., and supports functions such as code splitting and lazy loading.

Here is an example of a simple webpack config file:

const path = require('path');

module.exports = {
    
    
  entry: './src/index.js',
  output: {
    
    
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js'
  },
  module: {
    
    
    rules: [
      {
    
    
        test: /\.js$/,
        exclude: /node_modules/,
        use: {
    
    
          loader: 'babel-loader'
        }
      },
      {
    
    
        test: /\.css$/,
        use: ['style-loader', 'css-loader']
      },
      {
    
    
        test: /\.(png|jpg|gif)$/,
        use: ['file-loader']
      }
    ]
  }
};

9.3 Build tool: gulp

gulp is a stream-based automated build tool. It can help us automate and optimize various tasks in front-end development, such as file compression, image optimization, code merging, etc.

Here is an example of a simple gulp task:

const gulp = require('gulp');
const sass = require('gulp-sass');
const autoprefixer = require('gulp-autoprefixer');
const cssmin = require('gulp-cssmin');

gulp.task('styles', function() {
    
    
  return gulp.src('src/styles/*.scss')
    .pipe(sass())
    .pipe(autoprefixer())
    .pipe(cssmin())
    .pipe(gulp.dest('dist/styles'));
});

gulp.task('default', gulp.series('styles'));

9.4 Unit testing tools: Jest

Jest is a JavaScript-based unit testing framework developed by Facebook. It is simple to use and provides various functions and assertion libraries to write and run test cases.

Here is an example of a simple Jest test case:

function sum(a, b) {
    
    
  return a + b;
}

test('adds 1 + 2 to equal 3', () => {
    
    
  expect(sum(1, 2)).toBe(3);
});

Summarize:

This chapter introduces some commonly used front-end tools, including package management tool npm, module packaging tool webpack, construction tool gulp and unit testing tool Jest. These tools can help us improve the efficiency and quality of front-end development. By using these tools and choosing a suitable tool according to the needs of the project, you can better develop and maintain the front-end application. I hope you can become an efficient and excellent front-end developer by learning these tools.

Chapter 10 Front-end Performance Optimization Principles

In this chapter, we will introduce some basic principles of front-end performance optimization and provide some practical code examples.

10.1 Reduce HTTP requests

Reducing the number of HTTP requests required when a page loads is one of the important factors in improving performance. Here are some ways to reduce HTTP requests:

• Merge files: Merge multiple CSS or JavaScript files into one file to reduce the number of HTTP requests.

<link rel="stylesheet" href="styles.css">
<script src="scripts.js"></script>

• Use image sprites: Merge multiple small icons into one image, and use the CSS background-position property to display the desired icon.

.icon {
    
    
  background-image: url(sprites.png);
  background-position: -20px -40px;
}

10.2 Compressed files

Compressing CSS and JavaScript files can reduce file size, resulting in faster loading. Here are some ways to compress files:

• Remove Whitespace and Comments: Removes unnecessary whitespace and comments in CSS and JavaScript files.

/* 注释内容 */
body {
    
    
  color: red;
}

• Use compression tools: Use compression tools (such as UglifyJS, CleanCSS, etc.) to compress CSS and JavaScript files.

uglifyjs scripts.js -o scripts.min.js

10.3 Image Optimization

Optimizing images can reduce page load time. Here are some ways to optimize your images:

• Compress pictures: Use image compression tools (such as TinyPNG, ImageOptim, etc.) to compress pictures.

imageoptim image.png

• Choose an appropriate image format: Choose an appropriate image format, such as JPEG, PNG, or WebP, and use an appropriate quality setting.

<img src="image.jpg" alt="Image" />

10.4 Using the cache

Reasonable use of caching can reduce repeated network requests and improve page loading speed. Here are some ways to use caching:

• Set cache headers: Set appropriate cache headers on the server side so that browsers and proxy servers can cache resources.

Cache-Control: max-age=3600

• Use local cache: Use localStorage or sessionStorage to cache data on the client to reduce network requests.

// 存储数据
localStorage.setItem('data', JSON.stringify(data));

// 获取数据
var data = JSON.parse(localStorage.getItem('data'));

10.5 Lazy loading
Lazy loading can improve the initial loading speed of the page. Here are some lazy loading methods:

• Image lazy loading: Only load images when they appear in the visible area, instead of loading all images at once.

<img data-src="image.jpg" alt="Image" />

document.addEventListener('DOMContentLoaded', function() {
    
    
  var images = document.querySelectorAll('img[data-src]');
  for (var i = 0; i < images.length; i++) {
    
    
    if (elementInViewport(images[i])) {
    
    
      images[i].setAttribute('src', images[i].getAttribute('data-src'));
      images[i].removeAttribute('data-src');
    }
  }
});

Summarize:

This chapter introduces some basic principles of front-end performance optimization, including reducing HTTP requests, compressing files, optimizing images, using caches, and lazy loading. By following these principles and choosing the appropriate optimization method according to the needs of the project, you can improve the performance and user experience of the front-end application. I hope that by learning these optimization principles, you can become a developer who can write high-performance front-end code.

Chapter 11 Page Load Optimization

In this chapter, we'll cover some approaches to page load optimization and provide some practical code examples.

11.1 Properly aligning and compressing CSS and JavaScript

Properly arranging and compressing CSS and JavaScript files can reduce file size, resulting in faster page loads. Here are some optimization methods:

• Using external files: Put CSS and JavaScript code into external files and reference them using link and script tags.

<link rel="stylesheet" href="styles.css">
<script src="scripts.js"></script>

• Compressed files: Compress CSS and JavaScript files, removing unnecessary spaces and comments.

uglifyjs scripts.js -o scripts.min.js

11.2 Lazy loading non-critical resources

Lazy loading non-critical resources can improve the initial load speed of the page. Here are some lazy loading methods:

• Load JavaScript asynchronously: Set JavaScript code that does not affect the initial rendering of the page to load asynchronously.

<script async src="scripts.js"></script>

• Image lazy loading: Only load images when they enter the viewable area, instead of loading all images at once.

<img data-src="image.jpg" alt="Image" />

document.addEventListener('DOMContentLoaded', function() {
    
    
  var images = document.querySelectorAll('img[data-src]');
  for (var i = 0; i < images.length; i++) {
    
    
    if (elementInViewport(images[i])) {
    
    
      images[i].setAttribute('src', images[i].getAttribute('data-src'));
      images[i].removeAttribute('data-src');
    }
  }
});

11.3 Using caches and CDNs

Reasonable use of caching and CDN (Content Delivery Network) can reduce repeated network requests and improve page loading speed. Here are some ways to use caching and CDNs:

• Set cache headers: Set appropriate cache headers on the server side so that browsers and proxy servers can cache resources.

Cache-Control: max-age=3600

• Use CDN: Deploy static resources (such as CSS, JavaScript, and images) to CDN to improve resource loading speed.

<link rel="stylesheet" href="https://cdn.example.com/styles.css">
<script src="https://cdn.example.com/scripts.js"></script>
<img src="https://cdn.example.com/image.jpg" alt="Image">

11.4 Using preloading and prerendering

Using preloading and prerendering can obtain resources in advance and prerender the page when the page is loaded, thereby speeding up the user's access experience. Here are some ways to use preloading and prerendering:

• Preload resources: Use rel="preload" to preload important CSS and JavaScript files.

<link rel="preload" href="styles.css" as="style">
<link rel="preload" href="scripts.js" as="script">

• Prerender pages: Use rel="prerender" to prerender important pages.

<link rel="prerender" href="https://example.com/important-page.html">

Summarize:

This chapter introduces some methods of page load optimization, including proper arrangement and compression of CSS and JavaScript, lazy loading of non-critical resources, using caching and CDN, and using preloading and prerendering. By following these optimization methods, and choosing the appropriate method based on the needs of your project, you can greatly improve page loading speed and user experience. I hope that by learning these optimization principles, you can become a front-end developer who can optimize page load.

Chapter 12 Front-end debugging skills and tools

In this chapter, we will introduce some tips and common tools for front-end debugging, and provide some practical code examples.

12.1 Use console.log for log output

console.log is one of the most commonly used front-end debugging tools, which can output information to the browser's console. Here are some examples using console.log:

var name = "John";
console.log("Hello, " + name);

12.2 Using breakpoint debugging tools

The breakpoint debugging tool can help us pause the execution of the code when it reaches the specified position, and view the value of the variable, the call stack and other information. The following are some commonly used breakpoint debugging tools:

• Browser developer tools (such as Chrome DevTools): Set breakpoints in source code and view variable values ​​and call stacks through the debug panel.

function add(a, b) {
    
    
  debugger; // 在这里设置断点
  return a + b;
}

12.3 Using bug tracking tools

Error tracking tools can help us find errors in the code and provide useful error messages. Here are some commonly used bug tracking tools:

• Error stack: View the error stack information in the browser's console or in the server-side error log to see where and why the error occurred.

function divide(a, b) {
    
    
  if (b === 0) {
    
    
    throw new Error("Cannot divide by zero");
  }
  return a / b;
}

12.4 Using performance analysis tools

Profiling tools can help us find performance bottlenecks in our code and provide information about function execution times, resource loading times, and more. The following are some commonly used performance analysis tools:

• Browser's Performance Dashboard: Record and analyze page performance data in Chrome DevTools' Performance Dashboard.

console.time("myFunction"); // 开始计时
myFunction();
console.timeEnd("myFunction"); // 结束计时并输出执行时间

Summarize:

This chapter introduces some front-end debugging skills and common tools, including using console.log for log output, using breakpoint debugging tools, using error tracking tools, and using performance analysis tools. By mastering these debugging techniques and tools and using them flexibly during the development process, you can troubleshoot problems more easily and improve code quality and performance. I hope you can become an efficient and excellent front-end developer by learning these debugging skills.

Chapter 12 Front-end debugging skills and tools

In this chapter, we will introduce some tips and common tools for front-end debugging, and provide some practical code examples.

12.1 Use console.log for log output

console.log is one of the most commonly used front-end debugging tools, which can output information to the browser's console. Here are some examples using console.log:

var name = "John";
console.log("Hello, " + name);

12.2 Using breakpoint debugging tools

The breakpoint debugging tool can help us pause the execution of the code when it reaches the specified position, and view the value of the variable, the call stack and other information. The following are some commonly used breakpoint debugging tools:

• Browser developer tools (such as Chrome DevTools): Set breakpoints in source code and view variable values ​​and call stacks through the debug panel.

function add(a, b) {
    
    
  debugger; // 在这里设置断点
  return a + b;
}

12.3 Using bug tracking tools

Error tracking tools can help us find errors in the code and provide useful error messages. Here are some commonly used bug tracking tools:

• Error stack: View the error stack information in the browser's console or in the server-side error log to see where and why the error occurred.

function divide(a, b) {
    
    
  if (b === 0) {
    
    
    throw new Error("Cannot divide by zero");
  }
  return a / b;
}

12.4 Using performance analysis tools

Profiling tools can help us find performance bottlenecks in our code and provide information about function execution times, resource loading times, and more. The following are some commonly used performance analysis tools:

• Browser's Performance Dashboard: Record and analyze page performance data in Chrome DevTools' Performance Dashboard.

console.time("myFunction"); // 开始计时
myFunction();
console.timeEnd("myFunction"); // 结束计时并输出执行时间

Summarize:

This chapter introduces some front-end debugging skills and common tools, including using console.log for log output, using breakpoint debugging tools, using error tracking tools, and using performance analysis tools. By mastering these debugging techniques and tools and using them flexibly during the development process, you can troubleshoot problems more easily and improve code quality and performance. I hope you can become an efficient and excellent front-end developer by learning these debugging skills.

Chapter 14 Front-End Security Practices

In this chapter, we will introduce some practical methods of front-end security to help you improve the security of your application, and provide some code samples as a reference.

14.1 Input Validation and Filtering

User-entered data is always validated and filtered to prevent malicious code injection or other security risks. Here are some practical approaches to input validation and filtering:

• Validate the type and format of input data: Ensure that user-entered data is of the expected type and format.

var input = document.getElementById('inputField').value;
if (typeof input !== 'number') {
    
    
  alert('请输入数字');
}

• Filter special characters: Remove special characters in user input to prevent malicious code injection.

var input = document.getElementById('inputField').value;
var sanitizedInput = input.replace(/[<>&]/g, '');

14.2 Use a secure communication protocol

Use secure communication protocols (such as HTTPS) to encrypt data transmission to avoid man-in-the-middle attacks and data leakage. Here is an example using HTTPS:

<form action="https://example.com/login" method="post">
  <!-- 表单内容 -->
</form>

14.3 Implement permission control

Implement proper permission controls in applications to ensure only authorized users can access and perform sensitive operations. Here is an example of a basic permission control:

function deletePost(postId, userId) {
    
    
  if (userHasPermission(userId)) {
    
    
    // 执行删除操作
    deletePostFromDatabase(postId);
  } else {
    
    
    alert('您没有权限执行此操作');
  }
}

14.4 Preventing cross-site scripting attacks (XSS)

To prevent cross-site scripting attacks, some precautions should be taken such as escaping user input, using safe DOM manipulation methods, etc. Here's an example of escaping user input:

var userInput = "<script>alert('XSS attack');</script>";
var escapedUserInput = escapeHTML(userInput);

document.getElementById('content').innerHTML = escapedUserInput;

function escapeHTML(input) {
    
    
  return input.replace(/[&<>"']/g, function (match) {
    
    
    return {
    
    
      '&': '&amp;',
      '<': '&lt;',
      '>': '&gt;',
      '"': '&quot;',
      "'": '&#39;'
    }[match];
  });
}

Summarize:

This chapter introduces some front-end security practices, including input validation and filtering, using secure communication protocols, enforcing permission control, and preventing XSS attacks. By adopting these security practices and choosing the appropriate method based on the needs of your project, you can improve the security of your application and protect your users' data and privacy. I hope you can become a developer who pays attention to front-end security by learning these security practices.

Chapter 15 Getting Started with Cross-Platform Development

In this chapter, we will introduce the concept of cross-platform development and some common cross-platform development frameworks, and provide some code samples to help you get started with cross-platform development.

15.1 Overview of cross-platform development

Cross-platform development refers to using the same code to develop applications on different operating systems and devices. This saves development time and costs while enabling applications to run on multiple platforms. Here are some common cross-platform development approaches:

• Native development tools: Use cross-platform native development tools (such as React Native, Flutter) to develop applications.
• Hybrid Development Framework: Use a web technology-based hybrid development framework (such as Ionic, Cordova) to develop applications.
• Game engine: Use game engines (such as Unity, Cocos2d-x) to develop cross-platform game applications.

15.2 React Native example

React Native is a popular cross-platform development framework that allows you to develop native mobile applications using JavaScript. Here's a simple React Native example:

import React from 'react';
import {
    
     View, Text } from 'react-native';

export default function App() {
    
    
  return (
    <View style={
    
    {
    
     flex: 1, justifyContent: 'center', alignItems: 'center' }}>
      <Text>Hello, React Native!</Text>
    </View>
  );
}

15.3 Flutter example

Flutter is an open-source UI toolkit for building cross-platform mobile, web, and desktop applications. Here is a simple Flutter example:

import 'package:flutter/material.dart';

void main() {
    
    
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
    
    
  @override
  Widget build(BuildContext context) {
    
    
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Text('Hello, Flutter!'),
        ),
      ),
    );
  }
}

15.4 Ionic example

Ionic is an open-source UI framework based on web technologies for developing cross-platform mobile and desktop applications. Here is a simple Ionic example:

<ion-header>
  <ion-toolbar>
    <ion-title>
      Hello, Ionic!
    </ion-title>
  </ion-toolbar>
</ion-header>

<ion-content>
  <ion-card>
    <ion-card-header>
      <ion-card-title>Card Title</ion-card-title>
    </ion-card-header>
    <ion-card-content>
      This is some card content.
    </ion-card-content>
  </ion-card>
</ion-content>

Summarize:

This chapter introduces the concept of cross-platform development and common cross-platform development frameworks, including React Native, Flutter, and Ionic. By learning the basic usage of these frameworks and choosing a suitable cross-platform development method according to project requirements, you will be able to develop applications for different platforms more efficiently. I hope you can become an excellent developer of multi-platform applications by learning cross-platform development.

Chapter 16 Front-end Engineering and Modularization

In this chapter, we will introduce the concepts of front-end engineering and modularization, as well as some common front-end engineering and modularization tools, and provide some code examples to help you understand these concepts.

16.1 Overview of front-end engineering

Front-end engineering refers to the process of using a series of tools and methods to improve the efficiency, quality and maintainability of front-end development. Here are some common front-end engineering practices:

• Automated construction: Use construction tools (such as Webpack, gulp) to automate operations such as file compression, merging, and packaging.
• Continuous Integration and Deployment: Use continuous integration and deployment tools such as Jenkins, Travis CI to automate building, testing and deploying applications.
• Code quality inspection: Use static code analysis tools (such as ESLint, stylelint) to check code specifications and potential problems.

16.2 Modular overview

Modularization is the method of dividing a large codebase into smaller, more independent modules for easier management and reuse. Here are some common front-end modularization specifications and tools:

• CommonJS: Use require and module.exports syntax to import and export modules.

// math.js
function add(a, b) {
    
    
  return a + b;
}

module.exports = add;

// main.js
const add = require('./math');

console.log(add(2, 3)); // 输出：5

• ES Modules: Use the import and export syntax to import and export modules.

// math.js
export function add(a, b) {
    
    
  return a + b;
}

// main.js
import {
    
     add } from './math';

console.log(add(2, 3)); // 输出：5

16.3 Webpack Example

Webpack is a popular front-end build tool that allows you to package front-end resources into modular files. Here is a simple Webpack example:

// webpack.config.js
const path = require('path');

module.exports = {
    
    
  entry: './src/index.js',
  output: {
    
    
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js',
  },
};

// src/index.js
import {
    
     add } from './math';

console.log(add(2, 3)); // 输出：5

Bundle src/index.js and its dependencies into a dist/bundle.js file by running the Webpack build command.

16.4 Babel Example
Babel is a widely used JavaScript compiler that can convert the latest version of JavaScript into a backward compatible version. Here is a simple Babel example:

// index.js
const arr = [1, 2, 3];
const doubledArr = arr.map((num) => num * 2);

console.log(doubledArr); // 输出：[2, 4, 6]

By configuring Babel, convert the above code into backward compatible ES5 syntax.

Summary:
This chapter introduces the concepts and common tools of front-end engineering and modularization, including automated construction, continuous integration and deployment, code quality inspection, CommonJS, ES Modules, Webpack and Babel, etc. By using these tools and practices, you can develop and manage front-end projects more efficiently, and improve code maintainability and quality. I hope you can become an excellent front-end engineer by learning front-end engineering and modularization.

Chapter 17 Front-End Design Patterns and Best Practices

In this chapter, we will introduce some common front-end design patterns and best practices to help you write maintainable, scalable, and high-quality front-end code, and provide some code examples to illustrate these concepts.

17.1 Singleton pattern

The singleton pattern means that a class can only create one instance and provide a global access point to obtain the instance. Here is a simple singleton example:

class Singleton {
    
    
  constructor() {
    
    
    if (!Singleton.instance) {
    
    
      Singleton.instance = this;
    }

    return Singleton.instance;
  }
}

const instance1 = new Singleton();
const instance2 = new Singleton();

console.log(instance1 === instance2); // 输出：true

17.2 Observer pattern

Observer mode means that when the state of an object changes, all objects that depend on it will receive notifications and update automatically. Here is a simple observer pattern example:

class Subject {
    
    
  constructor() {
    
    
    this.observers = [];
  }

  addObserver(observer) {
    
    
    this.observers.push(observer);
  }

  notify(message) {
    
    
    this.observers.forEach((observer) => observer.update(message));
  }
}

class Observer {
    
    
  update(message) {
    
    
    console.log(`收到通知：${
      
      message}`);
  }
}

const subject = new Subject();
const observer1 = new Observer();
const observer2 = new Observer();

subject.addObserver(observer1);
subject.addObserver(observer2);

subject.notify('状态已更新');

17.3 Best Practice: Modular Development

Modular development is a development method that divides the code into independent and reusable modules to improve the maintainability and testability of the code. Here is an example of best practice modular development:

// math.js
export function add(a, b) {
    
    
  return a + b;
}

export function subtract(a, b) {
    
    
  return a - b;
}

// main.js
import {
    
     add, subtract } from './math';

console.log(add(2, 3)); // 输出：5
console.log(subtract(5, 2)); // 输出：3

17.4 Best Practice: Error Handling

Good error handling is key to writing robust front-end code. The following is an example of best practice error handling:

try {
    
    
  // 可能会抛出错误的代码
  throw new Error('发生错误');
} catch (error) {
    
    
  // 错误处理代码
  console.error('捕获到错误：', error);
}

Summarize:

This chapter introduces some common front-end design patterns and best practices, including singleton pattern, observer pattern, modular development, and error handling. By adopting these design patterns and best practices, you can write more maintainable, scalable and high-quality front-end code, improving development efficiency and code quality. I hope you can become a good front-end developer by learning these concepts.

Chapter 18 Front-end automated testing

In this chapter, we will introduce the importance of front-end automated testing and some common front-end automated testing tools and techniques, and provide some code examples to help you understand these concepts.

18.1 The importance of front-end automated testing

Front-end automated testing is the process of verifying the correctness, reliability, and performance of front-end code by writing automated test scripts. Here are some of the importance of front-end automated testing:

• Improve quality: Automated testing can cover code more comprehensively, reduce potential bugs, and improve code quality.
• Accelerated development: Automated testing can quickly find problems during the development process, reduce manual debugging time, and speed up iteration.
• Low maintenance cost: Automated testing can help quickly locate problems and verify whether the functions are normal after code changes, reducing the workload of manual regression testing.

18.2 Front-end automated testing tools and techniques

Here are some common front-end automation testing tools and techniques:

• Unit testing: Use frameworks such as Jest, Mocha, etc. to perform unit testing for functions, classes, and modules.

// math.js
export function add(a, b) {
    
    
  return a + b;
}

// math.test.js
import {
    
     add } from './math';

test('add()函数能够正确地进行加法运算', () => {
    
    
  expect(add(2, 3)).toBe(5);
});

• Integration testing: Use tools such as Selenium, Puppeteer, etc. to conduct automated integration testing of the entire application.

// app.test.js
describe('应用程序顶级UI是否正常工作', () => {
    
    
  beforeEach(async () => {
    
    
    await page.goto('http://localhost:3000');
  });

  it('首页是否显示正确的标题', async () => {
    
    
    const title = await page.$eval('.title', (e) => e.textContent);
    expect(title).toBe('欢迎来到我的应用程序');
  });
});

18.3 Jest Example

Jest is a popular JavaScript testing framework for writing unit and integration tests. Here is a simple Jest example:

// math.js
export function add(a, b) {
    
    
  return a + b;
}

// math.test.js
import {
    
     add } from './math';

test('add()函数能够正确地进行加法运算', () => {
    
    
  expect(add(2, 3)).toBe(5);
});

18.4 Puppeteer example

Puppeteer is an automated testing tool based on Chrome Headless, which can simulate user operations in real browsers. Here is a simple Puppeteer example:

const puppeteer = require('puppeteer');

async function runTest() {
    
    
  const browser = await puppeteer.launch();
  const page = await browser.newPage();

  await page.goto('http://www.example.com');
  const pageTitle = await page.title();

  console.log(`页面标题：${
      
      pageTitle}`);

  await browser.close();
}

runTest();

Summarize:

This chapter introduces the importance of front-end automated testing and common front-end automated testing tools and technologies, including unit testing, integration testing, Jest, and Puppeteer. By adopting these tools and techniques, you can write more reliable and high-quality front-end code, and improve development efficiency and code maintainability. I hope you can become an excellent front-end developer by learning front-end automated testing.

Appendix A: Common front-end resources and recommended learning materials

In this appendix, we will recommend some common front-end resources and learning materials for you to further study and improve. These resources include websites, blogs, books, and online courses.

1. Front-end development website

• MDN Web Documentation (https://developer.mozilla.org)
• W3Schools (https://www.w3schools.com)
• CSS-Tricks (https://css-tricks.com)
• Smashing Magazine (https://www.smashingmagazine.com)

2. Front-End Development Blog

• CSS Tricks (https://css-tricks.com)
• Scotch.io (https://scotch.io)
• SitePoint (https://www.sitepoint.com)
• David Walsh Blog (https://davidwalsh.name)

3. Front-End Development Books

• "JavaScript Advanced Programming" ("Professional JavaScript for Web Developers")
• JavaScript Definitive Guide ("JavaScript: The Definitive Guide")
• 《CSS揭秘》(《CSS Secrets: Better Solutions to Everyday Web Design Problems》)
• "Front-end Architecture: From Entry to Micro Front-end" ("Front-end Architecture: From Entry to Micro Front-end")

4. Online Courses and Tutorials

• freeCodeCamp (https://www.freecodecamp.org)
• Udemy (https://www.udemy.com)
• Coursera (https://www.coursera.org)
• Codecademy (https://www.codecademy.com)

5. Front-end development communities and forums

• Stack Overflow (https://stackoverflow.com)
• GitHub (https://github.com)
• Reddit r/webdev (https://www.reddit.com/r/webdev)
• CSS-Tricks Forums (https://css-tricks.com/forums)

The above resources can help you gain knowledge and skills in the field of front-end development, solve problems and communicate with other developers. Remember to choose suitable resources according to your interests and learning needs, and continue to learn and practice to continuously improve your front-end skills. I wish you success in your front-end development journey!

Appendix B: Analysis of common front-end interview questions

In this appendix, we will analyze some common front-end interview questions for you to help you better prepare for the interview. The questions touch on HTML, CSS, JavaScript, and other aspects of front-end development.

1. Parsing: What is the box model?
   The box model means that in the web page layout, each element is regarded as a rectangular box, including the content area, inner margin, border and outer margin. The box model in CSS can be controlled by the box-sizing property, which is content-box by default.

2. Parsing: What is a closure? What is it for?
   A closure is a function defined inside a function, and the inner function can access the variables of the outer function. Closures can be used to create private variables and functions, and can extend the lifetime of variables.

3. Parsing: What is event bubbling and event capture?
   Event bubbling means that the event is triggered from the most specific element, and then propagates up to the parent element until it reaches the root element of the document. The event capture starts from the root element of the document and propagates down to the most specific element.

4. Analysis: How to implement browser caching?
   Browser caching can be implemented by setting Cache-Control and Expires in the HTTP response header. Cache-Control specifies the rules of the cache, such as public or private, etc., and Expires sets the expiration time of the cache.

5. Analysis: What is a cross-domain request? How to solve the cross-domain problem?
   A cross-domain request refers to a request sent through XMLHttpRequest or Fetch API in a browser, and its target address is different from the domain name, protocol or port of the current page. Cross-domain problems can be solved through CORS (Cross-Origin Resource Sharing), and cross-domain requests can also be implemented using JSONP, proxy servers, or modifying server configuration.

The above are the analysis of some common front-end interview questions, hoping to help you better understand and prepare for the interview. Remember to combine real programming experience with deep learning to improve your overall understanding and ability to answer these questions. Good luck with your front-end interviews!

conclusion

Thank you for reading this book. Front-end development is a constantly evolving and changing field. Learning and mastering front-end skills requires continuous effort and practice.

In this book, we've covered the basics of front-end development, common techniques and tools, and some best practices and coding tips. We hope that these contents are helpful to your study and practice, and can stimulate your creativity and innovation spirit.

Whether you are just getting started learning front-end development, or a developer with some experience, remember to keep expanding your knowledge and skills. You'll keep improving yourself by participating in open source projects, reading great code, solving real problems, and interacting with other developers.

If you have any questions or need further assistance, please feel free to ask me. As a smart assistant, I will try my best to provide you with accurate and useful answers.

Finally, I wish you success in your front-end development journey! May your code be elegant, your web pages beautiful, and your user experiences amazing. Thanks!