<html><body>电子邮件：<input type="email" id="myEmail" value="billgates@example.com"><p>单击该按钮可更改电子邮件字段的默认值。</p><button onclick="myFunction()">试一试</button><p id="demo"></p><script>function myFunction() { document.getElementById("myEmail").defaultValue = "stevejobs@w3school.com.cn";}</script></body></html>