// React v16.2 
// ReactBaseClasses.js

/**
 * Base class helpers for the updating state of a component.
 */
function PureComponent(props, context, updater) {
  // Duplicated from Component.
  this.props = props;
  this.context = context;
  this.refs = emptyObject;
  // We initialize the default updater but the real one gets injected by the
  // renderer.
  this.updater = updater || ReactNoopUpdateQueue;
}

function ComponentDummy() {}
ComponentDummy.prototype = Component.prototype;
var pureComponentPrototype = (PureComponent.prototype = new ComponentDummy());
pureComponentPrototype.constructor = PureComponent;
// Avoid an extra prototype jump for these methods.
Object.assign(pureComponentPrototype, Component.prototype);
pureComponentPrototype.isPureReactComponent = true;

問題在于為什么要造一個(gè)ComponentDummy
我的理解是如果為了繼承prototype的話下面沒必要再用assign再設(shè)置一遍方法，他既然用了繼承了，這邊注釋說為了避免方法額外的原型查找才用的assign，既然這樣的話寫成下面這樣不就好了嗎

var pureComponentPrototype = PureComponent.prototype;
Object.assign(pureComponentPrototype, Component.prototype);
pureComponentPrototype.isPureReactComponent = true;