js自定義綁定事件

function Boy() {
    this._events = {};//定義的是對象
}
Boy.prototype.on = function (eventName, callback) {
    if (this._events[eventName]) {//不是第一次
        let flag = false;
        this._events[eventName].forEach((cb) => {
            if (cb == callback) flag = true;
        })
        if (!flag) {//防止重複綁定
            this._events[eventName].push(callback);
        }
    } else {
        this._events[eventName] = [callback];
    }
};
Boy.prototype.emit = function (eventName) {
    if (this._events[eventName]) {
        this._events[eventName].forEach(cb => cb())
    }
};

let play = function () {
    console.log("玩")
};

let eat = function () {
    console.log("吃")
};

let test = () => {
    console.log("測試箭頭函數")
}

let boy = new Boy();
boy.on('doPlay', play);
boy.on('doPlay', test);
boy.emit('doPlay');