<form action="/dy/html/getpost">

搜索: <input type="search" id="mySearch" name="filter" required>

<input type="submit">

</form>

<p>点击 "点我" 按钮查看在表单提交前搜索字段是否为必填字段</p>

<button onclick="myFunction()">点我</button>

<p id="demo"></p>

<script>

function myFunction() {

    var x = document.getElementById("mySearch").required;

    document.getElementById("demo").innerHTML = x;

}

</script>

​