js - Basics - Code World

table of Contents

Introduction 1. js
2. js manner of introduction
3. js statement
4. Variable

js (Javascript) - scripting language

Introduction 1. js

Javascript is an interpreted programming language that runs in the browser.

Javascript can be implemented on complex functions page, page impressions no longer a simple simple static information, but the implementation of the updated content, interactive maps, 2D / 3D animation, scrolling audio and video, etc.

Why do we have to learn Javascript?

1. Because you have no choice. In the web world, Javascript can only cross-platform, cross-browser web drive, interact with the user.
ActionScript 2.Flash behind used to be popular for a while, but with the rise of mobile applications, and no one with Flash to develop mobile App, so it is now marginalized.
3. Conversely, as more and more popular in HTML5 and mobile PC side, JavaScript has become more important. In addition, the emerging Node.js JavaScript into the server side, JavaScript has become a versatile player.

JavaScript version:

ECMAScript 4.1 (referred to ES4)
The latest version of the ECMAScript 6 standard (referred to as ES6)

2. js manner of introduction

1. inline js formula

<p id="" class="" style="" onclick="console.log(2);">mjj</p>
<!--console.log() 在控制台打印  onclick='' 单击，加事件：在<p>标签上加一个单击时执行在控制台打印的时间-->

2. The embedded js

<body>
<script type="text/javascript">
    //js代码
</script>
</body>

3. External js

<!--可以放在html内的任意位置-->
<script type="text/javascript" src="js/index.js"></script>
<!--在外部的js文件中写js代码-->

3. js statement

Javascript code to every word; as the end of the current statement.

1. Comment

// a single line comment
/ ** / multi-line comment, multi-line comments shortcuts: ctrl + shift + /

2. Test Statement

console.log('hello world');  //在控制台打印内容
alert('hello world');  //弹出框显示内容
console.log(window);  //打印window对象
prompt(message:'请输入今天的天气？');  //在弹出框内输入内容，prompt会有一个返回值，命名一个对象（变量）来接收，变量命名格式：使用var关键字 + 变量名
var name = prompt('请输入今天的天气？');  //接收prompt的返回值
console.log(name);  //打印name对象

3. assignment operator - increment and decrement operators

<script>
    var a = 1;
    a ++;  // 相当于a+=1;
    console.log(a);

    var a = 4;
    //先将a的值赋值给c，再计算a++
    var c = a ++;
    console.log(c);//4
    console.log(a);//5
    //先计算a++，再将a的值赋值给c
    var c = ++a;
    console.log(c);//5
    console.log(a);//5
</script>

4. Variable

Variables are divided into: basic data types, reference data types

4.1 Basic Data Types

Basic data types include: number (integer), string (string), Boolean (Boolean), undefined (undefined), null (empty object)

var a = 2;
var b = '2' + a;  //不会报错，一个字符串+一个数字会默认将数字转成字符串再拼接
var c = true;
console.log(typeof b);  //打印变量的类型

//先声明后定义——undefined
var e;
console.log(e);//查看值：undefined
console.log(typeof e);//查看类型：是undefined
var f = null;
console.log(f);
console.log(typeof  f);

Note: In Print Console: Integer blue, black string

4.2 reference data types

Reference data types comprising: Array (Array), Object (Object), function (function), Date (date object)

var arr = ['张三','李四'];
console.log(arr);

//定义在对象中的函数，叫做对象的方法
var obj = {
    name:'mjj',
    age:19,
    fav:function () {
        console.log(this); //存放对象的属性
    }
};
obj.fav();

js - Basics