**文件路徑** ``` packages/react/src/ReactBaseClasses.js ``` **源碼解析** ``` function Component(props, context, updater) { this.props = props; this.context = context; // If a component has string refs, we will assign a different object later. this.refs = emptyObject; // We initialize the default updater but the real one gets injected by the // renderer. this.updater = updater || ReactNoopUpdateQueue; } ``` ~~~ Component.prototype.setState = function(partialState, callback) { 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.', ); this.updater.enqueueSetState(this, partialState, callback, 'setState'); }; ~~~ > enqueueSetState是在react-dom實現的 > updater是為了兼容平臺 **forceUpdate** 強制react-component更新一遍，即便state沒有更新 ~~~ Component.prototype.forceUpdate = function(callback) { this.updater.enqueueForceUpdate(this, callback, 'forceUpdate'); }; ~~~ **PureComponent** 可以認為PureComponent繼承自Component ~~~ function ComponentDummy() {} ComponentDummy.prototype = Component.prototype; function PureComponent(props, context, updater) { 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; } const pureComponentPrototype = (PureComponent.prototype = new ComponentDummy()); pureComponentPrototype.constructor = PureComponent; // Avoid an extra prototype jump for these methods. Object.assign(pureComponentPrototype, Component.prototype); pureComponentPrototype.isPureReactComponent = true; //標示是PureComponent ~~~