代理绑定的情况下，点击一次“激活”，触发了两次回调。普通绑定不会出现这种情况。

<ul id="box">
    <li id="active">激活</li>
    <li>取消</li>
    <li>取消</li>
</ul>

function myBindEvent(element, type, selector, cb) {
    if (typeof selector === 'function') {
        cb = selector;
        selector = null;
    }
    element.addEventListener(type, event => {
        const target = event.target;
        console.log('selector:', selector)
        if (selector) {
            //  代理
            if (target.matches(selector)) {
                console.log(1)
                cb.call(target, event)
            }
        } else {
            //  普通
            console.log(2)
            cb.call(target, event)
        }
    }, true)
}

const box = document.getElementById('box');
myBindEvent(box, 'click', '#active', function (e) {
    e.stopPropagation()
    e.preventDefault()
    console.log(this.innerHTML)
})
myBindEvent(box, 'click', function (e) {
    console.log(this.innerHTML)
})