今天随手写个发布订阅的 event.js

相信大家对发布订阅肯定很熟悉吧，很多场景都应用到了发布订阅；

例如自定义的一些事件，通过自定义的‘事件’，通过某个点触发；

例如：promise的原理其实和发布订阅也有一些的关系；将成功，失败，或者的必须做的函数分别放在数组中，当promise返回成功时，则把成功的函数事件全部都发布出去；

今天我给大家写个发布订阅的event.js  ；相信有去看各种插件源码都可以看到这个文件

  function Event(){
                this._events={};
            }
            Event.prototype.on = function (type, fn, context = this) {
                if (!this._events[type]) {
                    this._events[type] = []
                }

                this._events[type].push([fn, context])
            }

            Event.prototype.once = function (type, fn, context = this) {
                function magic() {
                    this.off(type, magic)

                    fn.apply(context, arguments)
                }
                // To expose the corresponding function method in order to execute the off method
                magic.fn = fn

                this.on(type, magic)
            }

            Event.prototype.off = function (type, fn) {
                let _events = this._events[type]
                if (!_events) {
                    return
                }

                let count = _events.length
                while (count--) {
                    if (_events[count][0] === fn || (_events[count][0] && _events[count][0].fn === fn)) {
                        _events[count][0] = undefined
                    }
                }
            }

            Event.prototype.trigger = function (type) {
                let events = this._events[type]
                if (!events) {
                    return
                }

                let len = events.length
                let eventsCopy = [...events]
                for (let i = 0; i < len; i++) {
                    let event = eventsCopy[i]
                    let [fn, context] = event
                    if (fn) {
                        fn.apply(context, [].slice.call(arguments, 1))
                    }
                }
            }

demo：

            var bs=new Event();
            bs.on('click',function(){console.log(111)},window);
            var aaa=333;
            bs.on('click',function(){console.log(this.aaa)},window);
            bs.once('click',function(){console.log('once')},window);
            console.log(bs._events)
            bs.trigger('click')

            console.log(bs._events)
            bs.trigger('click')
            console.log(bs._events)

结果截图：