<html>
<body>
Homepage: <input type="url" id="myURL" maxlength="30">
<p>点击按钮获取 URL 字段maxlength属性值。</p>
<button onclick="myFunction()">点我</button>
<p id="demo"></p>
<script>
function myFunction() {
var x = document.getElementById("myURL").maxLength;
document.getElementById("demo").innerHTML = x;
}
</script>
</body>
</html>