自訂驗證：在input 加上
oninvalid="setCustomValidity('這個欄位必填');" oninput="setCustomValidity('');"
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<!-- Bootstrap CSS -->
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.1/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-F3w7mX95PdgyTmZZMECAngseQB83DfGTowi0iMjiWaeVhAn4FJkqJByhZMI3AhiU" crossorigin="anonymous">
<!-- Option 1: Bootstrap Bundle with Popper -->
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.1/dist/js/bootstrap.bundle.min.js" integrity="sha384-/bQdsTh/da6pkI1MST/rWKFNjaCP5gBSY4sEBT38Q/9RBh9AH40zEOg7Hlq2THRZ" crossorigin="anonymous"></script>
<title>表單</title>
</head>
<body>
<div class="container">
<h1 class="text-center">HTML 表單語法 測試 </h1>
<form action="接收表單目的" method="post" id="myForm" enctype="multipart/form-data" class="form-horizontal">
<!-- input text 文字方塊(單行)-->
<div class="mb-3">
<label for="name" class="form-label">姓名</label>
<input type="text" name='name' value='' class="form-control" id="name" aria-describedby="nameHelp" required>
<div id="nameHelp" class="form-text">請輸入姓名(網頁無障礙語法)</div>
</div>
<!-- input url 網址 -->
<div class="mb-3">
<label for="url" class="form-label">網址</label>
<input type="url" name="url" value='' class="form-control" id="url" aria-describedby="urlHelp" >
<div id="urlHelp" class="form-text">請輸入網址</div>
</div>
<!-- input email EMAIL-->
<div class="mb-3">
<label for="email" class="form-label">EMAIL</label>
<input type="email" name="email" value='' class="form-control" id="email" aria-describedby="emailHelp" >
<div id="emailHelp" class="form-text">請輸入EMAIL</div>
</div>
<!-- input password 密碼 -->
<div class="mb-3">
<label for="password" class="form-label">Password</label>
<input type="password" name="password" value='' class="form-control" id="password">
</div>
<!-- input date 日期方塊 -->
<div class="mb-3">
<label for="date" class="form-label">日期方塊</label>
<input type="date" name="date" value='' class="form-control" id="date">
</div>
<!-- input date 年月方塊 -->
<div class="mb-3">
<label for="month" class="form-label">年月方塊</label>
<input type="month" name="month" value='' class="form-control" id="month">
</div>
<!-- input week 年週方塊-->
<div class="mb-3">
<label for="week" class="form-label">年週方塊</label>
<input type="week" name="week" value='' class="form-control" id="week">
</div>
<!-- input number 數字方塊-->
<div class="mb-3">
<label for="number" class="form-label">數字方塊</label>
<input type="number" name="number" value='' class="form-control" id="number">
</div>
<!-- input color 顏色選擇器-->
<div class="mb-3">
<label for="color" class="form-label">顏色選擇器</label>
<input type="color" name="color" value='#000000' class="form-control" id="color">
</div>
<!-- input search 搜尋方塊-->
<div class="mb-3">
<label for="search" class="form-label">搜尋方塊</label>
<input type="search" name="search" value='' class="form-control" id="search">
</div>
<!-- input range 滑動方塊-->
<div class="mb-3">
<label for="range" class="form-label">滑動方塊</label>
<input type="range" name="range" value='' class="form-control" id="range" min="0" max="100" value="90" step="1">
</div>
<!-- 單選 -->
<div class="mb-3">
<label class="form-label w-100">單選</label>
<div class="form-check form-check-inline">
<input type="radio" name="radio" value='單選1' class="form-check-input" id="radio_1">
<label class="form-check-label" for="radio_1">單選1</label>
</div>
<div class="form-check form-check-inline">
<input type="radio" name="radio" value='單選2' class="form-check-input" id="radio_2" checked>
<label class="form-check-label" for="radio_2">單選2</label>
</div>
<div class="form-check form-check-inline">
<input type="radio" name="radio" value='單選3' class="form-check-input" id="radio_3">
<label class="form-check-label" for="radio_3">單選3</label>
</div>
</div>
<!-- 多選 -->
<div class="mb-3">
<label class="form-label w-100">多選</label>
<div class="form-check form-check-inline">
<input type="checkbox" name="checkbox" value='多選1' class="form-check-input" id="checkbox_1">
<label class="form-check-label" for="checkbox_1">多選1</label>
</div>
<div class="form-check form-check-inline">
<input type="checkbox" name="checkbox" value='多選2' class="form-check-input" id="checkbox_2" checked>
<label class="form-check-label" for="checkbox_2">多選2</label>
</div>
<div class="form-check form-check-inline">
<input type="checkbox" name="checkbox" value='多選3' class="form-check-input" id="checkbox_3">
<label class="form-check-label" for="checkbox_3">多選3</label>
</div>
</div>
<!-- 下拉選單 -->
<div class="mb-3">
<label class="form-label">下拉選單</label>
<select name="select" class="form-select" id="select">
<option value="下拉選單1">下拉選單1</option>
<option value="下拉選單2" selected>下拉選單2</option>
<option value="下拉選單3">下拉選單3</option>
</select>
</div>
<!-- 選單(多選) -->
<div class="mb-3">
<label class="form-label">下拉選單(多選)</label>
<select name="select_m" class="form-select" id="select_m" multiple>
<option value="下拉選單(多選)1">下拉選單(多選)1</option>
<option value="下拉選單(多選)2" selected>下拉選單(多選)2</option>
<option value="下拉選單(多選)3">下拉選單(多選)3</option>
</select>
</div>
<!-- 文字區域(多行) -->
<div class="mb-3">
<label class="form-label">文字區域</label>
<textarea name="textarea" class="form-control" id="textarea" rows="5" >文字區域</textarea>
</div>
<!-- 隱藏-->
<input type="hidden" name='op' value='set_sheet' class="form-control" id="op" >
<button type="submit" class="btn btn-primary w-100">送出</button>
</form>
</div>
</body>
</html>