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源代码：
点击运行
<!DOCTYPE html> <html> <body> <form action="form-action.php"> 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> </body> </html>
运行结果
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