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关于EventBus事件总线

• 事件总线，实现 on, once, emit, off
  • on, once 是注册函数，存储起来
  • emit时找到对应的函数，执行
  • off找到对应的函数，从对象中删除
• 注意
  • 区分on和once
  • on绑定的事件可连续执行，除非off
  • once绑定的函数 emit 一次即删除，也可未执行而被 off
  • 数据结构上标识出 on 和 once

实现方案1

代码实现：使用参数区分 on和once

class EventBus {/*{key1: [{fn: fn1, isOnce: false},{fn: fn2, isOnce: false},{fn: fn3, isOnce: true},],key2: []}*/private events: {[key: string]: Array<{fn: Function; isOnce: boolean}>}constructor() {this.events = {};}on(type: string, fn: Function, isOnce: boolean = false) {const events = this.events;if (events[type] == null) {events[type] = []; // 初始化 key 的 fn 数组}events[type].push({fn, isOnce});},// 这里是初步版本once_origin(type: string, fn: Function) {const events = this.events;if (events[type] == null) {events[type] = []; // 初始化 key 的 fn 数组}events[type].push({fn, isOnce: true});},once(type: string, fn: Function, isOnce: boolean = false) {this.on(type, fn, true);},off(type: string, fn?:Function) {if (!fn) {// 解绑所有 type 的函数this.events[type] = [];} else {// 解绑单个 fnconst fnList = this.events[type];if (fnList.length) {this.events[type] = fnList.filter(item.fn !== fn);}}},emit(type: string, ...args: any[]) {const fnList = this.events[type];if (fnList == null) return;// 注意this.events[type] = fnList.filter(item => {const { fn, isOnce } = item;fn(...args);// 处理once, 它执行一次就要被过滤掉if (!isOnce) return true;return false;})}
}const e = new EventBus();
function fn1(a: any, b: any) {console.log('fn1', a, b)};
function fn2(a: any, b: any) {console.log('fn2', a, b)};
function fn3(a: any, b: any) {console.log('fn3', a, b)};e.on('key1', fn1);
e.on('key1', fn2);
e.once('key1', fn3);e.emit('key1', 10, 20); // 触发 fn1, fn2, fn3
e.off('key1', fn1);
e.emit('key1', 100, 200); // 触发 fn2

实现方案2

代码实现: 拆分保存 on和once

class EventBus {private events: { [key: string]: Array<Function>} // {key1: [fn1, fn2]}private onceEvents: {[key: string]: Array<Function>} // 结构同上constructor() {this.events = {}; // 存储 onthis.onceEvents = {}; // 存储 once}// on 触发on(type: string, fn: Function) {const events = this.events;if (events[type] === null) events[type] = [];events[type].push(fn);},once(type: string, fn: Function) {const onceEvents = this.onceEvents;if (onceEvents[type] === null) onceEvents[type] = [];onceEvents[type].push(fn);},// 解绑事件off(type: string, fn: Function) {if (!fn) {// 解绑所有事件this.events[type] = [];this.onceEvents[type] = [];} else {// 解绑单个const fnList = this.events[type];const onceFnList = this.onceEvents[type];if (fnList.length) {this.events[type] = fnList.filter(curFn => curFN!== fn);}if (onceFnList.length) {this.onceEvents[type] = onceFnList.filter(curFn => curFN!== fn);}}},emit(type: string, ...args: any[]) {const fnList = this.events[type];const onceFnList = this.onceEvents[type];if (fnList.length) {fnList.forEach(f => f(...args));}if (onceFnList.length) {onceFnList.forEach(f => f(...args));// once 执行一次就删除，这里更简单，代码更简洁this.onceEvents[type] = [];}}
}// 测试用例同上，此处省略

总结

• 区分 on, once
• 合理的数据结构，比算法优化更有效