【前端成长之路】实现Emitter

[AmamiyaCx]

class Emitter {
    constructor() {
        this.emitter = {};
    }

    // 触发事件，传入参数
    emit(name, ...args) {
        const callbacks = this.emitter[name];
        if (callbacks) {
            callbacks.forEach(callback => {
                callback.apply(this, args);
            });
        }
    }

    // 监听事件，执行回调
    on(name, cb) {
        const callbacks = this.emitter[name];
        if (callbacks) {
            this.emitter[name].push(cb);
        } else {
            this.emitter[name] = [cb];
        }
    }

    // 卸载事件
    off(name, cb) {
        const callbacks = this.emitter[name];
        if (callbacks) {
            let index = callbacks.findIndex(item => item === cb);
            this.emitter[name].splice(index, 1);
        }
    }

    // 只执行一次，然后删除
    once(name, cb) {
        const fn = (...args) => {
            cb.apply(this, args);
            this.off(name, fn);
        }
        this.on(fn, cb);
    }
}