alpha方法掛在實(shí)例上

beta方法掛在原型上

它們打印出來(lái)的this卻完全不同

alpha打印出來(lái)是APP實(shí)例

beta打印出來(lái)是button元素

沒(méi)想明白是為什么

<button id="aa">aa</button>
<button id="bb">bb</button>
<script type="text/javascript">
    class APP {
        constructor() {
            this.alpha = () => {
                console.log(this);
            }
            const $aa = document.querySelector('#aa');
            const $bb = document.querySelector('#bb');
            $aa.addEventListener('click', this.alpha);
            $bb.addEventListener('click', this.beta);
        }

        beta() {
            console.log(this);
        }
    }

    new APP();
</script>