react源码阅读笔记：二、关于 React.createElement

函数定义

const ReactElement = function(type, key, ref, self, source, owner, props) { ... }

1. ReactElement是个啥

  /**
    * Factory method to create a new React element. This no longer adheres to
    * the class pattern, so do not use new to call it. Also, instanceof check
    * will not work. Instead test $$typeof field against Symbol.for('react.element') to check
    * if something is a React Element.
    *
    **/

根据注释说明：ReactElement是一个创建React元素的工厂方法，简言之就是React类型的元素对象就是ReactElement,再具体一点的东西到后面再进行分析。

1. 关于ReactElement方法的参数 type, key, ref, owner, props不多说
   1. self 用来检测this和owner的不同，用在dev环境里面，调用React.createElement的时候从config中取出来的。
   2. source 用来标注文件名，行号和其它信息的参数，也只用在dev环境里面
2. 关于此函数的返回值 ReactElement的返回值是一个如下的对象

     const element = {
    // This tag allows us to uniquely identify this as a React Element
    $$typeof: REACT_ELEMENT_TYPE,
   
    // Built-in properties that belong on the element
    type: type,
    key: key,
    ref: ref,
    props: props,
   
    // Record the component responsible for creating this element.
    _owner: owner,
     };
   

   $$typeof用来标识此对象是否是一个ReactElement元素