Table of contents
51. What is SEO and how to optimize it?
52. What is compatibility problem and how to solve it?
53. How to implement an asynchronous queue?
54. What is Virtual DOM? How to optimize the performance of Virtual DOM?
55. What is Webpack and how to use it?
56. How to optimize HTTP request speed?
57. What is XSS (cross-site scripting attack)? How to prevent it?
58. What is Web Worker? How to use it?
59. What are TCP and UDP? What are their differences?
60. What is WebRTC? How to use it?
51. What is SEO and how to optimize it?
SEO (Search Engine Optimization) is search engine optimization, which is used to improve website ranking and weight, thereby gaining more exposure and traffic in search engines. Optimizing SEO can start from the following aspects:
● Website content optimization: including producing high-quality original content, updating website content, increasing the number of website pages, etc.
● Website structure optimization: including optimizing website navigation, setting image ALT tags, rational use of H tags, etc.
● Website code optimization: including reducing the amount of web page code, reducing HTTP requests, optimizing JavaScript and CSS codes, etc.
● Website performance optimization: including accelerating website access speed, optimizing website response time, improving website accessibility, etc.
● External link optimization: including increasing external links, strengthening internal links, participating in social media, etc.
52. What is compatibility problem and how to solve it?
Compatibility issues refer to problems caused by different browsers or terminal devices implementing different Web standards. To solve compatibility issues, you can start from the following aspects:
● Use standard Web technologies and syntax and avoid using code that is specific to a particular browser.
● Use tools such as CSS Reset and Normalize.css to circumvent browser default style differences.
● Use tools such as Modernizr and HTML5 Shiv to resolve insufficient browser support for HTML5 and CSS3.
● Automatically add browser prefixes using tools such as Autoprefixer and PostCSS.
● Use tools such as polyfill and es6-shim to solve browser incompatibility issues with ES6.
53. How to implement an asynchronous queue?
Asynchronous queue is a data structure used to process asynchronous tasks. It is mainly used to ensure that asynchronous tasks are executed in a specific order. The following two options can be used to implement asynchronous queues:
● Use callback functions: Connect asynchronous tasks in series through callback functions to ensure that asynchronous tasks are executed in a specific order.
● Use Promise and async/await: Implement chain calls of asynchronous tasks through Promise and async/await to ensure that asynchronous tasks are executed in a specific order.
54. What is Virtual DOM ? How to optimize the performance of Virtual DOM ?
Virtual DOM is a middle-layer structure that uses JavaScript objects to represent real DOM objects. It is used to optimize DOM operations and improve rendering efficiency.
Optimizing the performance of Virtual DOM can start from the following aspects:
● Avoid frequently creating and destroying Virtual DOM objects.
● Use key attributes to optimize the rendering of Virtual DOM to avoid unnecessary redrawing and rearrangement.
● Reduce the number of comparisons of Virtual DOM, which can be achieved through shouldComponentUpdate and PureComponent.
● Choose an appropriate synthetic event mechanism to avoid unnecessary browser redraws.
● Use native DOM API when necessary to avoid frequent updates of Virtual DOM
55. What is Webpack and how to use it?
Webpack is a tool for packaging, compiling, and compressing JavaScript applications. It can package multiple modules into one or more files according to dependencies.
Using Webpack you can perform the following operations:
● Module packaging and compilation: Webpack can be used to package and compile JavaScript modules, CSS files, image files and other resource files.
● Plug-in extension: Using Webpack, you can use different plug-ins to extend functions, such as extracting public modules, code compression, version control, etc.
● Build tool extension: Using Webpack, you can combine different build tools, such as Gulp, Grunt, npm, etc., to achieve a more flexible build process.
● Integrated development environment: Webpack can be integrated into development tools, such as WebStorm, VSCode, etc., to bring a more efficient development experience.
56. How to optimize HTTP request speed?
HTTP (Hyper Text Transfer Protocol) protocol is a communication protocol used to transmit data on the Web, including request and response parts.
Optimizing HTTP request speed can start from the following aspects:
● Use the HTTP2 protocol: The HTTP2 protocol supports features such as multiplexing and header compression, which can reduce request response delays and network load.
● Reduce the number of HTTP requests: You can reduce the number of HTTP requests by merging CSS, JS and other files, compressing images, etc.
● Reasonable use of cache: Set the cache policy by setting the Cache-Control, Expires and other attributes in the HTTP request header to avoid unnecessary requests.
● Optimize HTTP request headers: By reducing the size of HTTP request headers and avoiding the use of long-lived Cookies and Sessions, the HTTP request speed can be optimized.
● Use CDN server: By using CDN (Content Delivery Network) server, you can speed up the response speed of HTTP requests and improve user experience.
57. What is XSS ( cross- site scripting attack ) ? How to prevent it ?
XSS is a web security vulnerability that allows attackers to inject malicious script code to attack machines and data.
XSS attacks can be divided into three types: storage type, reflection type and DOM Based.
Preventing XSS attacks can start from the following aspects:
1. Filter user input: Escape special characters in user input, such as <, >, &, etc., to prevent attackers from injecting malicious script code.
2. Use the HTTPOnly attribute: Setting the cookie to the HTTPOnly attribute can prevent attackers from accessing the cookie content through JavaScript.
3. Use Content Security Policy (CSP): The data source of the page can be restricted through the CSP protocol, thereby effectively preventing XSS attacks.
4. Avoid using eval and new Function: The eval and new Function functions can execute JavaScript code and are vulnerable to attacks and should be avoided.
58. What is Web Worker? How to use it?
Web Worker is a browser API used to run JavaScript scripts in background threads without blocking the execution of the foreground thread.
Web Worker can create multiple threads (to make full use of CPU performance on multi-core CPUs), and can communicate messages with the main thread. Using Web Worker can improve the response speed of the page and avoid long-term computing tasks causing the UI interface to become unresponsive.
59. What are TCP and UDP? What are their differences?
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are commonly used transmission protocols in the Internet.
TCP is a reliable, connection-oriented data transmission protocol with features such as data integrity, reliability, and flow control;
UDP is a stateless, connectionless data transmission protocol with the characteristics of fast transmission speed and high efficiency.
The difference between TCP and UDP can be summarized as follows:
● TCP is connection-oriented, but UDP is not connection-oriented.
● TCP has reliability, but UDP does not.
● TCP has flow control and congestion control, but UDP does not.
●TCP is usually used for applications that require reliable transmission, such as HTTP and FTP, and UDP is usually used for real-time applications, such as video streaming, online games, etc.
60. What is WebRTC? How to use it?
WebRTC (Web Real-Time Communication) is a technical protocol that supports real-time audio and video communication between Web browsers. It relies on the implementation of the browser itself and does not require the installation of additional plug-ins or applications.
WebRTC can transmit streaming media and data directly between browsers, thereby supporting browser-based real-time communication applications such as VolP, video conferencing, and screen sharing.
WebRTC can achieve the following functions:
● Network connection establishment and management.
● Video and audio codec, real-time voice and video streaming.
● NAT penetration technology solves the dynamic allocation of IP addresses and communication problems in NAT network environment.
● Reliable and unreliable data transmission channels.