DOM是事件监听器
DOM事件监听器予许一个事件触发多个方法，在实际工作中应用比较多。
<!DOCTYPE html>
<html>
<head>
<title>DOM事件监听器1</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<button id='a'>按钮</button>
<script>
var elbtn = document.getElementById('a');
elbtn.addEventListener('click', msg, false);
function msg(){
alert("DOM事件监听器");
}
</script>
</body>
</html>
在监听器中调用到参数函数
<!DOCTYPE html>
<html>
<head>
<title>DOM事件监听器2</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<button id="a">按钮</button>
<script>
var elbtn = document.getElementById('a');
elbtn.addEventListener('click', function () {
say('DOM');
}, false);
function say(name) {
alert('你好,' + name + "！");
}
</script>
</body>
</html>