<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title><!-- 放在头部 --><!-- 页面加载完执行 --><script>/* 匿名函数 */window.onload = function() {/* alert('加载完成'); */var oBtn = document.getElementById('btn');//没点击就调用oBtn.onclick = function() {alert(1);}}</script>
</head><body><!-- 点击按钮 弹出1 --><input type="button" value="变红" id="btn"></body></html>运行结果
