<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>Document</title>
</head>
<body>
<button id="btn1">按钮1</button>
<button id="btn2">按钮2</button>
<button onclick="demo()">按钮3</button>
<script type="text/javascript" >
const btn1 = document.getElementById('btn1')
btn1.addEventListener('click',()=>{
alert('按钮1被点击了')
})
const btn2 = document.getElementById('btn2')
btn2.onclick = ()=>{
alert('按钮2被点击了')
}
function demo(){
alert('按钮3被点击了')
}
</script>
</body>
</html>