React -- a simple implementation of render & create element

nameIsZoe27 2021-05-03 11:26:45
react simple implementation render create


At present, the company's technology stack is still based on React Mainly , I saw a lot of jd They all need to know the source code, and even need to be able to write simple source code implementation , Do as you say

initialization react project

  1. cnpm i create-react-app -g
  2. create-react-app myReact
  3. Delete all irrelevant files Just leave the entry file


4. my react The version is 17.0.2

  • 4.1 17 After the jsx Compilation no longer generates React.createElement
  • 4.2 Is in babel Compile phase automatically import {jsx} from “react/jsx-runtime” jsx() replace createElement , The purpose may be to decouple , You don't have to do it in the project import React from "react";
  • 4.3 script Will be in the jsx() Ban Because you have to do it yourself createElement Method

 Disable NEW jsx conversion .png

  • 4.4 npm run eject The pit of , No pop-up configuration operation , as a result of react17 To change the jsx Conversion rules Need to be in script in set DISABLE_NEW_JSX_TRANSFORM=true , To disable jsx(), However, after pop-up configuration, it will be disabled all the time and will not succeed Packing will report an error ( Also left a hole , I didn't find out why the pop-up was disabled all the time )

React.createElement Realization

  1. createElement effect

    Generate vdom Used to do render Parameters

  2. determine createElement Enter the reference

babel Compiler tools


  1. createElement The ginseng
  • type: Label type
  • props: Tag properties and children Elements
  1. createElement The process
 * @param type Element type
* @param config The configuration object of the element
* @param children The children of the element
function createElement(type, config, children) {
// deconstruction config
let props = { ...config };
// The method of judgment is taken into consideration length ,
// Greater than 3 Then there are sub elements ( Child elements with labels )
if (arguments.length > 3) {
// Get child elements
children =, 2);
props.children = children;
return {
const React = { createElement };
export default React;
 Copy code 

React.render The implementation of the

  1. Ideas
  • vdom Become real dom
  • fictitious dom Property synchronization to real dom
  • recursive childrenDom
  • append To the target container
  1. Implementation process
  • render Method to do :vdom Transforming reality DOM
* @param vdom Virtual objects to render
* @param container append The target container node for
function render(vdom, container) {
//vdom Transforming reality DOM
const dom = function(vdom){
//vdom The type of : character string , Numbers , Directly back to the text node
if(typeof vdom === "string" || typeof vdom === "number"){
// Otherwise it's a virtual object --- namely :react Elements Return the corresponding label
let { type, props } = vdom;
let dom = document.createElement(type);
// by dom Set the style style,className
// Judge props.children type
if (
typeof props.children === "string" ||
typeof props.children === "number"
//children It's just documents
dom.textContent = props.children;
}else if (typeof props.children === "object" && props.children.type) {
//children Also a vdom
// recursive render, The target container becomes itself to do the following append
render(props.children, dom);
} else if (Array.isArray(props.children)) {
// Processing of multiple sub elements
//for loop In turn, calls render();
return dom;
 Copy code 

call render,reateElement

import ReactDOM from "./react-dom";
className: "title",
style: {
color: "red",
React.createElement("span", null, "hello"),
 Copy code 



Source code git Address

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