事件只綁定一次的實現

const one = (element, events, handler) => {
    let executed = false;
    let eventsArray = [];
    if (/array/i.test(Object.prototype.toString.call(events))) {
        eventsArray = events;
    } else {
        eventsArray.push(events);
    }

    // 事件觸發時執行，執行過程當中解綁，並改變標記變量executed的狀態
    const onceHanler = e => {
        if (executed) {
            return;
        }

        eventsArray.forEach(eventName => element.removeEventListener(eventName, onceHanler, false));
        handler(e);
        executed = true;
    }

    eventsArray.forEach(eventName => element.addEventListener(eventName, onceHanler, false));
}

one(element, ['animationend', 'webkitAnimationEnd', 'mozAnimationEnd'], handler);