【js】手写封装简易版监听器

    class EventEmitter {
        constructor() {
            this.events = {}
        }
        // 添加订阅
        on(type, callback) {
            if (!this.events[type]) {
                this.events[type] = []
            }
            this.events[type].push(callback)
        }
        // 触发事件
        emit(type, ...rest) {
            if (!this.events[type]) throw new Error('event does not exist')
            console.log(this.events[type])
            this.events[type].forEach((fn) => fn.apply(this, rest))
        }
        // 移除订阅
        off(type, callback) {
            if (!this.events[type]) throw new Error('event dose not exist')
            this.events[type] = this.events[type].filter((item) => item !== callback)
        }

        // 只触发一次事件，之后销毁
        once(type, callback) {
            const fn = () => {
                this.off(type, fn)
                callback(...arguments)
            }
            this.on(type, fn)
        }
    }

    const myEvent = new EventEmitter()

    myEvent.on('click', (res) => {
        console.log('监听click事件', res)
    })

    myEvent.once('click',function(){
        console.log('click2')
    })
    myEvent.emit('click', 'click data')