<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>W3Cschool教程(w3cschool.cn)</title>
</head>
<body>
<input type="number" id="myNumber" placeholder="Quantity">
<p>点击按钮修改 number 字段的提示信息。</p>
<button onclick="myFunction()">点我</button>
<p id="demo"></p>
<script>
function myFunction() {
document.getElementById("myNumber").placeholder = "Amount";
}
</script>
</body>
</html>
