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

This time I bring you the latest front-end interview questions in 2018. We know that interviews are an indispensable 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 process. The interview is a big challenge. Let’s take a look.

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

1. Please name three ways to reduce page loading time. (Loading time refers to perceived time or actual loading time)

1. Reduce HTTP requests;
2. Merge and compress Js/css files;
3. Use cache manifest;
4. Turn on gzip on the server side;
5. Using CDN, users can obtain the resources they need nearby, the access speed is guaranteed, and the stability is guaranteed
6. Put external JS and CSS aside
7. Operate the DOM as little as possible. Some DOM that require repeated operations can be placed in variables

2. Please describe pseudo-elements (pseudo-elements) and their uses.

Pseudo-classes are used to select information that does not exist in the DOM tree and are not easily found by conventional selectors:hover :active :focus :link
Pseudo-elements are used to apply certain special effects Add to the selector; such as::before::after
Pseudo elements are used to express non-text and decorative things, which is conducive to HTMLsemantic;

3. Do you have experience with retina screen compatibility? If so, what technology is used where?

Taobao's lib-flexible library;

4. Why should you use translate() instead of absoluteposition, or vice versa? Why?

In terms of animation, transform can allow the GPU to participate in calculations, resulting in higher FPS; absolute minimum animation unit is 1px, and transform can be smaller, making the animation smoother.
From other perspectives In other words, absolute must have a relative parent box;

5. How do you organize your code? Should I use the module pattern or the classic inheritance method? (This is the answer after Baidu)

Internal: module mode;
External: inheritance

6. Explanation of function foo() {} and var foo = function() {} The difference in usage

1. The function declaration must have a function name, 2. It can be called anywhere, that is, there is variable promotion
3.Function expressionThe two names before and after can be the same or different; 4. The name after the function expression can be omitted;
5. The name after the expression can only be used inside the function; 6. The function can only be used after it is declared Call

7. Please explain how JSONP works and why it is not true Ajax.

json is a data format; jsonp is a method of data calling;
1. Take advantage of the fact that the script tag has no cross-domain restrictions, create a script tag in the script, and the address points to Third-party API, such as
(the src attribute is not subject to cross-domain restrictions)
2. Provide acallback functionto receive data; the data generated by the third party is a package of json data, in the form of callback({"name":"hax","gender":"Male"} ), the callback function can pass callback=fn
3 through the URL parameter. In this way, the browser will call the callback function and pass the parsed json object as a parameter. The script of this website can process the incoming data in the callback function; ajax essentially obtains server information through You have mastered the case method. For more exciting information, please pay attention to other related articles on the PHP Chinese website!