2018 latest front-end interview questions four

This time we bring you the latest front-end interview questions in 2018. We know that before you enter a company, the interview stage is an essential part. This time, the common front-end interview questions are sorted and summarized to help you. Get over the hump of front-end interviews. Let’s take a look.

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

1. What is FOUC (flash without style content)? How do you avoid FOUC?

If you use the import method to import CSS, some pages will have some strange phenomena in Internet Explorer under Windows: the page content will flash without style for a moment. This phenomenon is called Flash of Unstyled Content, referred to as FOUC.

The reasons are roughly as follows:

1. Use the import method to import the style sheet.

          2. Place the style sheet at the bottom of the page

            3. There are several style sheets placed in different locations in the html structure.

In fact, the principle is very clear: when the style table is late than the structural HTML, when loading to this style table, the page will stop the previous rendering. After this style sheet is downloaded and parsed, the page will be re-rendered, resulting in a brief blurry screen phenomenon.

Solution:

Use the LINK tag to place the style sheet in the document HEAD.

2. Please explain what ARIA and screen readers are, and how to make the website accessible.

                                                                                              ARIA provide solutions for Web app to meet the different needs of users. Build a bridge between users and software.

The new HTML5 standard adds aria-* tag attributes, the full name is Accessible Rich Internet Application. Used in conjunction with the role tag attribute.

The role attribute indicates the actual role of a non-standard tag. For example, if you use a div as a button, then set the div's role="button", and the auxiliary tool can recognize that it is actually a button. The function of aria-* is to describe the specific information of this tag in the visual situation.

The simplest application is, for example,

The auxiliary tool will know that this div is actually a checkbox role and is in the selected state.

3. Please explain the advantages and disadvantages of CSS animation and JavaScript animation.

1. CSS3 animation is only compatible with Ie10+, js animation is compatible with almost all browsers;

2. JS animation is more flexible, CSS3 animation is simpler

3. JS animation has high reusability

  4. In terms of time scale, CSS animation granularity is relatively coarse, and JS animation can be finer;

  5. Browser CSS animation with poor frame rate can be done To degrade gracefully, additional code needs to be written for js code

6. Under certain conditions, css animation performance is better than JS animation; (for browsers with webkit kernel, js performs expensive tasks without causing layout and In the case of repaint)

7.css3 has natural time support such as (animationENd and transitionEnd)

4. What is cross-domain resource sharing (CORS)? What problem is it used to solve?

When using ajax cross-domain request, the browser reports an error: Modification in this way would require too much engineering effort, so CORS, a relatively simple and efficient technology, is used. Compared with JOSP, CORS is more efficient. JSONP can only implement GET requests due to its principle, while CORS supports all types of HTTP requests. Using CORS, you can use ordinary ajax to achieve cross-domain

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!

Related reading:

2018 latest front-end interview questions one

2018 latest front-end interview questions

2018 latest front-end interview questions three

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