2018 latest front-end interview questions six-JS Tutorial-php.cn

2018 latest front-end interview questions six

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Release： 2020-09-01 15:55:42

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This time we bring you the latest front-end interview questions in 2018. We know that interviews are an essential part of front-end work. This time, the common front-end interview questions are sorted and summarized to help you get through the front-end interview. Big trouble. Let’s take a look.

[Related recommendations: Front-end interview questions (2020)]

1. How do you optimize the files and resources of the website?

1. Reduce the number of http requests as much as possible, merge css, js, and pictures
2. Use CDN to reduce communication distance
3. Add Expire/Cache-Control header
4 .Enable Gzip compressed files
5.Put css at the top of the page
6.Put script at the bottom of the page

7.Avoid using expressions in css
8.Place css, js are placed in external files
9. Reduce DNS queries
10. Minimize css, js, reduce file size
11. Avoid redirection
12. Remove duplicate scripts
13. Configure entity tag ETag
14. Use AJAX cache to load website content in batches and update locally

2. Why is it more effective to use multiple domain names to provide website resources? How many resources can a browser download from one domain name at the same time?

1. Static content and dynamic content are stored on separate servers, and different servers are used to process requests. Processing of dynamic content only processes dynamic content and does not process anything else to improve efficiency, which makes CDN (content distribution network) caching more convenient
2. Break through the browser concurrency limit (you can just pick a G URL: https://lh4.googleusercontent.com/- si4dh2myPWk/T81YkSiAI/AAAAAAAAQ5o/LlwbBRpp58Q/w497-h373/IMG_20120603_163233.jpg, replace the lh4 in front with lh3, lh6 and so on, and you can still access it, like a map This is very important for sites like this that require a large number of concurrent downloads of images. )
3. Cookies will not be transferred across domains, saving bandwidth

3. Please write a simple slideshow effect page

<!DOCTYPE html>
<html>
<head>
<title>幻灯片</title>
<style type="text/css">
.myDiv{
    width:600px;
    height:400px;
   margin:20px auto;
   background-size:over;
   background-postion:center;
  -webkit-animation-name: "loop";
  -webkit-animation-duration:20s;
  -webkit-animation-iteration-count:infinite;
}
@-webkit-keyframes "loop"{
     0%{background:url(http://img5.duitang.com/uploads/blog/201408/12/20140812150016_8NMUU.jpeg) no-repeat;}
     25%{background:url(http://pic29.nipic.com/20130518/9908282_142904524164_2.jpg) no-repeat;}
     50%{background:url(http://uploadfile.huiyi8.com/2014/0605/20140605114503719.jpg) no-repeat;}
    75%{background:url(http://img3.redocn.com/20100322/Redocn_2010032112222793.jpg) no-repeat;}
    100%{background:url(http://uploadfile.huiyi8.com/2014/0605/20140605114447934.jpg)no-repeat;}
}
</style>
</head>

Copy after login

4. Please talk about your understanding of the importance of web standards and standard-setting organizations.

Web standards and standard-setting organizations are all intended to make the development of the web more "healthy". First, they constrain browser developers to follow unified standards, and secondly, they constrain website developers, thus reducing development difficulty and cost. SEO will also be better, and there will be no bugs or security issues caused by misuse of code, ultimately improving the usability of the website.

5. Please explain the advantages and disadvantages of CSS animation and JavaScript animation.
JS Animation
Disadvantages: (1) JavaScript runs in the main thread of the browser, and there are other JavaScript scripts, style calculations, layouts, drawing tasks, etc. that need to be run in the main thread, which interfere with the thread and cause Blocking may occur, resulting in frame loss.
(2) The complexity of the code is higher than that of CSS animation
Advantages: (1) JavaScript animation control capability is very strong, and the animation can be controlled during the animation playback process: start, pause, playback, terminate, and cancel. It can be done.
(2) Animation effects are richer than css3 animations. Some animation effects, such as curve movement, impact flicker, and parallax scrolling effects, can only be completed by JavaScript animation.
(3) CSS3 has compatibility issues , and JS most of the time does not have compatibility issues
CSS animation
Disadvantages: (1) The running process control is weak and event bindingcallback functions cannot be attached. CSS animations can only be paused, cannot find a specific time point in the animation, cannot reverse the animation halfway, cannot change the time scale, cannot add callback functions at specific positions or bind playback events, and there is no progress report
(2) The code is lengthy. If you want to use CSS to implement slightly more complex animations, the CSS code will become very cumbersome in the end.
Advantages: (1) The browser can optimize animations.
Browsers use a similar mechanism to requestAnimationFrame. Compared with setTimeout and setInterval, the main advantages of requestAnimationFrame in setting animations are: 1) requestAnimationFrame will concentrate all DOM operations in each frame and complete them in one redraw or reflow. , and the redraw or reflow time interval closely follows the browser's refresh frequency. Generally speaking, this frequency is 60 frames per second. 2) requestAnimationFrame will not redraw or reflow in hidden or invisible elements, which of course means less cpu, gpu and memory usage. Force the use of hardware acceleration (improve animation performance through GPU)

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the PHP Chinese website!