const SafeEventEmitter = require(‘safe-event-emitter‘)const ee = new SafeEventEmitter()ee.on(‘boom‘, () => { throw new Error() })ee.emit(‘boom‘) // no error here// error is thrown after setTimeout

const util = require(‘util‘)const EventEmitter = require(‘events/‘)var R = typeof Reflect === ‘object‘ ? Reflect : null ???//Reflect是对象则为R，否则R为nullvar ReflectApply = R && typeof R.apply === ‘function‘ ?//当R不为null且R.apply是函数时，ReflectApply为R.apply函数，否则就是定义的ReflectApply函数 ?? R.apply ?: function ReflectApply(target, receiver, args) { ???return Function.prototype.apply.call(target, receiver, args);}module.exports = SafeEventEmitterfunction SafeEventEmitter() { ?EventEmitter.call(this)}util.inherits(SafeEventEmitter, EventEmitter)SafeEventEmitter.prototype.emit = function (type) {//事件触发函数 ?// copied from https://github.com/Gozala/events/blob/master/events.js ?// modified lines are commented with "edited:" ?var args = []; ?for (var i = 1; i < arguments.length; i++) args.push(arguments[i]); //将传入的参数push进数组args ?var doError = (type === ‘error‘); //即事件的类型是否为“error” ?var events = this._events; ?if (events !== undefined)//当事件被定义了时，即调用过on()进行监听 ???doError = (doError && events.error === undefined); //事件为error但是events.error没有定义doError才返回true ?else if (!doError) //如果不是error事件则返回false ???return false; ?// If there is no ‘error‘ event listener then throw. ?if (doError) { //如果为error事件 ???var er; ???if (args.length > 0) //且有参数传入 ?????er = args[0]; //第一个参数应该为Error ???if (er instanceof Error) {//name就将错误抛出 ?????// Note: The comments on the `throw` lines are intentional, they show ?????// up in Node‘s output if this results in an unhandled exception. ?????throw er; // Unhandled ‘error‘ event ???} ???// At least give some kind of context to the user 否则就说明没有定义Error，那么下面就会定义相应的错误抛出 ???var err = new Error(‘Unhandled error.‘ + (er ? ‘ (‘ + er.message + ‘)‘ : ‘‘)); ???err.context = er; ???throw err; // Unhandled ‘error‘ event ?} ?var handler = events[type];//得到on()监听时定义的回调函数 ?if (handler === undefined)//如果回调没定义则返回false ???return false; ?if (typeof handler === ‘function‘) {//如果定义了则调用下面的safeApply（回调函数，上下文环境，参数） ???// edited: using safeApply ???safeApply(handler, this, args); ?} else { //如果回调不是一个函数，而是一个函数数组，则调用arrayClone（） ???var len = handler.length; ???var listeners = arrayClone(handler, len); ???for (var i = 0; i < len; ++i) ?????// edited: using safeApply ?????safeApply(listeners[i], this, args); ?} ?return true;}function safeApply(handler, context, args) {//就是在context这个上下文环境中，将相应的args参数传给handler回调函数，对回调函数进行调用 ?try { ???ReflectApply(handler, context, args) ?} catch (err) { //特别之处就在于在调用回调过程中如果出错了，错误先使用setTimeout压入堆栈，在整个回调函数调用完成后才抛出 ???// throw error after timeout so as not to interupt the stack ???setTimeout(() => { ?????throw err ???}) ?}}function arrayClone(arr, n) { ?var copy = new Array(n); ?for (var i = 0; i < n; ++i) ???copy[i] = arr[i]; ?return copy;}

Reflect.apply() ???????????????????????对一个函数进行调用操作，同时可以传入一个数组作为调用参数。和 Function.prototype.apply() 功能类似。Reflect.construct() ???????????????????对构造函数进行 new 操作，相当于执行 new target(...args)。Reflect.defineProperty() ??????????????和 Object.defineProperty() 类似。Reflect.deleteProperty() ??????????????作为函数的delete操作符，相当于执行 delete target[name]。Reflect.enumerate() ???????????????????该方法会返回一个包含有目标对象身上所有可枚举的自身字符串属性以及继承字符串属性的迭代器，for...in 操作遍历到的正是这些属性。Reflect.get() ?????????????????????????获取对象身上某个属性的值，类似于 target[name]。Reflect.getOwnPropertyDescriptor() ????类似于 Object.getOwnPropertyDescriptor()。Reflect.getPrototypeOf() ??????????????类似于 Object.getPrototypeOf()。Reflect.has() ?????????????????????????判断一个对象是否存在某个属性，和 in 运算符 的功能完全相同。Reflect.isExtensible() ????????????????类似于 Object.isExtensible().Reflect.ownKeys() ?????????????????????返回一个包含所有自身属性（不包含继承属性）的数组。Reflect.preventExtensions() ???????????类似于 Object.preventExtensions()。返回一个Boolean。Reflect.set() ?????????????????????????将值分配给属性的函数。返回一个Boolean，如果更新成功，则返回true。Reflect.setPrototypeOf() ??????????????类似于 Object.setPrototypeOf()。