实现发布订阅模式

.on('event', ()=>{})

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class EventEmitter {
    constructor() {
        this.events = []
    }

    on(name, fn) {
        if (this.events[name]) {
            this.events[name].push(fn)
        } else {
            this.events[name] = [fn]
        }
    }

    once(name, fn) {
        const onceFn = (data) => {
            fn(data)
            this.off(name, onceFn)
        }
        this.on(name, onceFn)
    }

    emit(name, data) {
        (this.events[name] || []).forEach(fn => fn(data))
    }

    off(name, fn) {
        const fns = this.events[name]
        if (!fns) {
            return
        }
        if (fn) {
            const index = fns.findIndex(f => f === fn)
            if (index > -1) {
                fns.splice(index, 1)
            }
        } else {
            delete this.events[name]
        }
    }
}

测试

JavaScript
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var em = new EventEmitter()

function test(data) {
    console.log('test', data)
}

em.on('onTest', test)
// em.once('onTest', test)

em.emit('onTest', {a: 1})

em.off('onTest', test)

em.emit('onTest', {a: 2})