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Preface

What is? css A block element ？

Block level elements are displayed on a single line . Its sibling element must not be in the same line as it is （ Unless out of the document stream ）. To put it more generally , It's a block element (block element) It's usually the container element of other elements , Can hold other block elements or inline elements .

css Three characteristics of block elements ：

• Each block level element is on its own line , The following elements can only start on another line , It's not possible for two elements to share one line .

• Height of element 、 Width 、 Row height and top bottom margin can be set .

• If the width of the element is not set , The default is the width of the parent element .

Basic knowledge

1.  distinguish Real DOM and Virtual DOM

| 

Real DOM

 | 

Virtual DOM

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 ----------------- ||  Update slow . |  Update faster . ||  It can be updated directly  HTML. |  Cannot update directly  HTML. ||  If the element is updated , Create a new DOM. |  If the element is updated , Update  JSX . || DOM The operation cost is very high . | DOM  The operation is very simple . ||  More memory consumed . |  Little memory consumption . |

2.  What is? React？

• React  yes  Facebook  stay  2011  The front end developed in  JavaScript  library .

• It follows a component-based approach , Help build reusable UI Components .

• It's used to develop complex and interactive  Web  And mobile  UI.

• Even though it's only in  2015  In open source , But there's a big support community .

3. React What are the characteristics of ？

React The main functions are as follows ：

1） It USES

fictitious DOM

  Not the real thing DOM.2） It can be used

Server-side rendering

.3） It follows

One way data flow

Or data binding .

4.  List React Some of the main advantages of .

React Some of the main advantages of ：

1） It improves the performance of the application 2） It can be easily used in the client and server 3） because  JSX, The code is very readable 4）React  It's easy with  Meteor,Angular  And so on 5） Use React, To write UI Test cases become very easy

5. React What are the limitations ？

React The restrictions are as follows ：

1）React  It's just a library , Not a complete framework 2） It has a huge library , It takes time to understand 3） Novice programmers can be hard to understand 4） Coding becomes complicated , Because it uses inline templates and  JSX

6.  What is? JSX？

JSX  yes J avaScript XML  Abbreviation . yes  React  A file used , It USES  JavaScript  The expressiveness and the like  HTML  Template syntax for . This makes  HTML  The document is very easy to understand . This file makes the application very reliable , And can improve its performance .

7.  You know  Virtual DOM  Do you ？ Explain how it works .

Virtual DOM  It's a lightweight  JavaScript  object , At first it was just  real DOM  Copy of . It's a node tree , It's going to take the elements 、 Their properties and contents as objects and their properties . React  The rendering function of is from  React  Create a node tree in the component . It then updates the tree in response to changes in the data model , The change is caused by various actions performed by the user or the system .

Virtual DOM  There are three simple steps in the working process .

1） Whenever the underlying data changes , Whole  UI  Will be in  Virtual DOM  Re render in description .2） And then before the calculation  DOM  The difference between the representation and the new representation .3） After the calculation , Will only be updated with the actual changes  real DOM.

8.  Why can't browsers read JSX？

Browsers can only handle  JavaScript  object , Instead of reading the general  JavaScript  Object  JSX. So in order for the browser to read  JSX, First , You need to use a picture  Babel  In this way  JSX  The converter will  JSX  The file is converted to  JavaScript  object , And then pass it to the browser .

Last

You have to ask whether front-end development is difficult , I have to say a common saying in the field of computer , This sentence is 『

It's not hard , It's not hard

』, For those who are not familiar with the technology in a certain field , Because I don't know, I have a sense of mystery , It's hard to be mysterious , That is to say 『 It's not hard 』; When you learn this technology , Know what technology can and can't do , It's just a matter of how long it takes to do it , It's not hard , So is 『 It's not hard 』.

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