setState

react/packages/react/src/ReactBaseClasses.js

/** * Sets a subset of the state. Always use this to mutate * state. You should treat `this.state` as immutable. * * There is no guarantee that `this.state` will be immediately updated, so * accessing `this.state` after calling this method may return the old value. * * There is no guarantee that calls to `setState` will run synchronously, * as they may eventually be batched together.  You can provide an optional * callback that will be executed when the call to setState is actually * completed. * * When a function is provided to setState, it will be called at some point in * the future (not synchronously). It will be called with the up to date * component arguments (state, props, context). These values can be different * from this.* because your function may be called after receiveProps but before * shouldComponentUpdate, and this new state, props, and context will not yet be * assigned to this. * * @param {object|function} partialState Next partial state or function to *        produce next partial state to be merged with current state. * @param {?function} callback Called after state is updated. * @final * @protected */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');};

SyntheticEvent

参考

react源码剖析——（二）解密setState机制