ReactBaseClasses

Component

// Component 类构造函数
function Component(props, context, updater) {
  // 初始化 props, context
  this.props = props;
  this.context = context;
  // If a component has string refs, we will assign a different object later.
  // 初始化 refs 为空对象
  this.refs = emptyObject;
  // We initialize the default updater but the real one gets injected by the
  // renderer.
  // 更新渲染用的函数 updater
  this.updater = updater || ReactNoopUpdateQueue;
}
// 用于判断当前函数是否是继承于 React.Component 的类组件
Component.prototype.isReactComponent = {};
Component.prototype.setState = function(partialState, callback) {
  // 类型校验
  invariant(
    typeof partialState === 'object' ||
      typeof partialState === 'function' ||
      partialState == null,
    'setState(...): takes an object of state variables to update or a ' +
      'function which returns an object of state variables.',
  );
  // 将数值更新操作入队
  this.updater.enqueueSetState(this, partialState, callback, 'setState');
};
Component.prototype.forceUpdate = function(callback) {
  // 将强制更新操作入队
  this.updater.enqueueForceUpdate(this, callback, 'forceUpdate');
};

PureComponent

function PureComponent(props, context, updater) {
  // 与 Component 一致
  this.props = props;
  this.context = context;
  // If a component has string refs, we will assign a different object later.
  this.refs = emptyObject;
  this.updater = updater || ReactNoopUpdateQueue;
}
// 一个跟 Component 完全一致的类（没有初始化的内容）
function ComponentDummy() {}
ComponentDummy.prototype = Component.prototype;
// 实现 PureComponent extends Component
const pureComponentPrototype = (PureComponent.prototype = new ComponentDummy());
pureComponentPrototype.constructor = PureComponent;
// Avoid an extra prototype jump for these methods.
Object.assign(pureComponentPrototype, Component.prototype);
// 判断当前组件是否是继承于 React.PureComponent 的类组件
pureComponentPrototype.isPureReactComponent = true;