给元素添加事件，为注册事件或者绑定事件
注册事件两种方式
eventTarget.addEventListener(type, listener, [useCapture])
evetagrget.attachEvent(eventNameWithOn, callback)
<body>
<button>传统注册事件</button>
<button>addEventListener ie9以上</button>
<button>attachEvent ie678</button>
<script>
var btns = document.querySelectorAll(‘button‘);
// 传统注册事件
btns[0].onclick = function () {
alert(‘传统方式‘)
};
// addEventListener 添加多个不覆盖
btns[1].addEventListener(‘click‘, function () {
alert(‘ddEventListener ie9以上‘)
});
btns[1].addEventListener(‘click‘, function () {
alert(‘ddEventListener ie9以上---2‘)
});
//attachEvent
btns[2].attachEvent(‘click‘, function () {
alert(‘attachEvent‘)
})
</script>
</body>
btns.onclick = null
eventTarget.removeEventListener(type, listener, [useCapture])
<body>
<button>addEventListener ie9以上</button>
<button>attachEvent ie678</button>
<script>
var btns = document.querySelectorAll(‘button‘);
// addEventListener 添加多个不覆盖
btns[0].addEventListener(‘click‘, fn);
function fn() {
alert(222);
this.removeEventListener(‘click‘, fn)
}
//attachEvent
btns[1].attachEvent(‘click‘, fn1);
function fn1() {
alert(111);
this.detachEvent(‘click‘, fn1)
}
</script>
</body>
原文：https://www.cnblogs.com/py-web/p/12218609.html