阅读react源码--createClass部分

var ReactClass = {
  createClass: function(spec) {
    // createClass实现
  },
  injection: {
    injectMixin: function(mixin) {
      injectedMixins.push(mixin)
    },
  },
}

var createClass = function(spec) {
  var Constructor = function(props, context, updater) {
    // 这段代码是不是很熟悉，跟component里的一样。
    this.props = props
    this.context = context
    this.refs = emptyObject
    this.updater = updater || ReactNoopUpdaterQueue

    // 获取初始化的state
    var initialState = this.getInitialState ? this.getInitialState() : null
    // getInitialState()必须返回对象
    !(typeof initialState === "object" && !Array.isArray(initialState))
      ? "提示报错"
      : void 0
    this.state = initialState

    // 继承ReactComponent，并重写replaceState和isMounted
    Constructor.prototype = new ReactClassComponent()
    Constructor.prototype.constructor = Constructor

    // mixin提前注入的对象,通过ReactClass.injection.injectMixin注入
    injectedMixins.forEach(mixSpecIntoComponent.bind(null, Constructor))
    // Mixin一些其他的属性
    mixSpecIntoComponent(Constructor, spec)

    // 赋值初始化的props
    if (Constructor.getDefaultProps) {
      Constructor.defaultProps = Constructor.getDefaultProps()
    }

    // 判断是否有render方法，没有就报错
    !Constructor.prototype.render ? "提示报错" : void 0

    // 赋值没有定义的默认的生命周期的函数为null
    for (var methodName in ReactClassInterface) {
      if (!Constructor.prototype[methodName]) {
        Constructor.prototype[methodName] = null
      }
    }
  }
  // 返回构造函数
  return Constructor
}

// Mixin replaceState和isMounted的对象
var ReactClassMixin = {
  replaceState: function(newState, callback) {
    this.updater.enqueueReplaceStaet(this.newState)
    if (callback) {
      this.updater.enqueueCallback(this, callback, "replaceState")
    }
  },
  isMounted: function() {
    return this.updater.isMounted(this)
  },
}

// 合并ReactComponent.prototype，和 ReactClassMixin
var ReactClassComponent = function() {}
Object.assign(
  ReactClassComponent.prototype,
  ReactComponent.prototype,
  ReactClassMixin
)

// 继承ReactClassComponent
Constructor.prototype = new ReactClassComponent()
Constructor.prototype.constructor = Constructor

var RESERVED_SPEC_KEYS={
  displayName:function(Constructor,displayName){
    Constructor.displayName=displayName;
  },
  mixins:function(Constructor,mixins){
    if(mixins){
      for(var i=0;i<mixins.length;i++){
        mixSpecIntoComponent(Constructor.mixins[i]);
      }
    }
  },
  childContextTypes:function(COnstrcutor,childContextTypes){
    //.....
  },
  contextTypes:function(Constructor,contextTypes){
    //......
  },
  getDefaultProps:function(Constructor,getDefaultProps){
    //....
  },
  propTypes:function(Constructor,propTypes){
    //....
  },
  statics:function(Constructor,statics){
    //....
  },
  autobind:function(){}
}
function mixSpecIntoComponent(Constructor,spec){
  // 如果spec中有mixins，则合并
  if(spec.hasOwnProperty('mixins')){
    RESERVED_SPEC_KEYS.mixins(Constructor,spec.mixins);
  }
  var proto=Constructor.prototype;
  for(var name in spec){
    if(!spec.hasOwnProperty(name)){
      continue;
    }
    if(name==='mixins'){
      // 第一步已经合并了mixins属性了，所以此处不需要再次合并
      continue;
    }
    var property=spec[name];
    // 合并保留的关键属性
    if(RESERVED_SPEC_KEYS.hasOwnProperty(name)){
      RESERVED_SPEC_KEYS[name](Constructor,property);
    }else{
      // 合并自定义的属性
      ....
    }

  }
}

var injection = {
  injectMixin: function(mixin) {
    injectedMixins.push(mixin)
  },
}