手写Eventbus

代码如下：

class EventEmitter {
    constructor() {
        this.events = this.events || new Map();
    }

    addListener(type, fn) {
        if (!this.events.has(type)) {
            this.events.set(type, fn);
        }
    }

    emit(type) {
        const fn = this.events.get(type);
        fn.apply(this, [...arguments].slice(1));
    }
}

const eventEmitter = new EventEmitter();
eventEmitter.addListener('add', function (a, b) {
    console.log(a + b);
});
eventEmitter.emit('add', 23, 22);