<body>
<button >按钮1</button>
<button >按钮2</button>
<button onclick="demo()">按钮3</button>
</body>
<script>
let btn1 = ('btn1')
('click', ()=>{
alert('按钮1被点击了')
})
let btn2 = ('btn2')
= ()=>{
alert('按钮2被点击了')
}
function demo(){
alert('按钮3被点击了')
}
</script>