1. 使用表单中的id属性获取表单中的数据

在表单的input标签中指定id属性值,在script脚本中可以通过 “表格的名称.id名称.value”来访问表单中的值,例如:register_form.username.value
表单代码:
<form name = "register_form" action="" method="post">

        昵称:<input type="text" name="username" maxlength="20" id="username"><br>
        真实姓名:<input type="text" name="realname" maxlength="20" id="realname"><br>
        性别: <input name ="sex" type ="radio"   value = "男" checked>
                男&nbsp;
              <input name ="sex" type ="radio"   value = "女" checked>
                女<br>
        密码:<input type="password" name="password1" maxlength="20"size="20"id="password1"><br>
        确认密码:<input type="password" name="password2" maxlength="20"size="20"id="password2"><br>
        请选择感兴趣的方向:<br/>
        <input type="checkbox" name="interest" value="体育">体育
        <input type="checkbox" name="interest" value="旅游">旅游
        <input type="checkbox" name="interest" value="听音乐">听音乐
        <input type="checkbox" name="interest" value="看书">看书<br>
        E—mail:<input name="email" type="text" id="PWD224" size="50"id="email"><br>

        <input name = "Submit" type = "button"   value = "保存" onclick = check()>
        <input name = "Reset" type = "reset" value = "重新填写">
</form>
在script脚本中,通过id访问表单中的值,利用函数判断其值是否为空,如果为空,则输出“请输入该信息字样”。
script脚本代码:
<script type="text/javascript">
    function check(){ 
	    if( register_form.username.value==""){
	        alert("请输入用户名!"); register_form.username.focus(); return;
	    }else if(register_form.realname.value=="") {
	        alert("请输入真实姓名!");register_form.realname.focus();return;
	    }else if(register_form.password1.value==""){
	        alert("请输入密码!"); register_form.password1.focus();return;
	    }else if(register_form.password2.value==""){
	        alert("请输入确认密码!");register_form.password2.focus(); return;
	    }else if(register_form.email.value==""){
	        alert("请输入邮箱!"); register_form.email.focus();return;
	    }else{
	        document.register_form.submit();
	    }
	}
运行结果:

在这里插入图片描述

完整的代码:
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>注册新用户</title>
    <script type="text/javascript">
    function check(){ 
	    if( register_form.username.value==""){
	        alert("请输入用户名!"); register_form.username.focus(); return;
	    }else if(register_form.realname.value=="") {
	        alert("请输入真实姓名!");register_form.realname.focus();return;
	    }else if(register_form.password1.value==""){
	        alert("请输入密码!"); register_form.password1.focus();return;
	    }else if(register_form.password2.value==""){
	        alert("请输入确认密码!");register_form.password2.focus(); return;
	    }else if(register_form.email.value==""){
	        alert("请输入邮箱!"); register_form.email.focus();return;
	    }else{
	        document.register_form.submit();
	    }
	}
    </script>
</head>
<body>
<h2>注册新用户</h2>
<form name = "register_form" action="" method="post">

        昵称:<input type="text" name="username" maxlength="20" id="username"><br>
        真实姓名:<input type="text" name="realname" maxlength="20" id="realname"><br>
        性别: <input name ="sex" type ="radio"   value = "男" checked>&nbsp;
              <input name ="sex" type ="radio"   value = "女" checked><br>
        密码:<input type="password" name="password1" maxlength="20"size="20"id="password1"><br>
        确认密码:<input type="password" name="password2" maxlength="20"size="20"id="password2"><br>
        请选择感兴趣的方向:<br/>
        <input type="checkbox" name="interest" value="体育">体育
        <input type="checkbox" name="interest" value="旅游">旅游
        <input type="checkbox" name="interest" value="听音乐">听音乐
        <input type="checkbox" name="interest" value="看书">看书<br>
        E—mail:<input name="email" type="text" id="PWD224" size="50"id="email"><br>

        <input name = "Submit" type = "button"   value = "保存" onclick = check()>
        <input name = "Reset" type = "reset" value = "重新填写">
</form>
</body>
</html>

2. getElementsByName()方法

因为一个文档中的 name 属性可能不唯一(如 HTML 表单中的单选按钮通常具有相同的 name 属性),所有 getElementsByName() 方法返回的是元素的数组,而不是一个元素。
例如,下面的代码可以获得form中第一个name为“inputText”的元素:
 var myParagragh = document.getElementsByName("inputText")[0].value; 
完整代码:
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>注册新用户</title>
    <script type="text/javascript" >
		function check(){ 
	    if( document.getElementsByName("username")[0].value==""){
	        alert("请输入用户名!"); return;
	    }else if(document.getElementsByName("realname")[0].value=="") {
	        alert("请输入真实姓名!"); return;
	    }else if(document.getElementsByName("password1")[0].value==""){
	        alert("请输入密码!"); return;
	    }else if(document.getElementsByName("password2")[0].value==""){
	        alert("请输入确认密码!"); return;
	    }else if(document.getElementsByName("email")[0].value==""){
	        alert("请输入邮箱!"); return;
	    }else{
	        document.register_form.submit();
	    }
	}
	</script>
</head>
<body>
<h2>注册新用户</h2>
<form name = "register_form" action="" method="post">

        昵称:<input type="text" name="username" maxlength="20"><br>
        真实姓名:<input type="text" name="realname" maxlength="20" id="realname"><br>
        性别: <input name ="sex" type ="radio"   value = "男" checked>&nbsp;
              <input name ="sex" type ="radio"   value = "女" checked><br>
        密码:<input type="password" name="password1" maxlength="20"size="20"><br>
        确认密码:<input type="password" name="password2" maxlength="20"size="20"><br>
        请选择感兴趣的方向:<br/>
        <input type="checkbox" name="interest" value="体育">体育
        <input type="checkbox" name="interest" value="旅游">旅游
        <input type="checkbox" name="interest" value="听音乐">听音乐
        <input type="checkbox" name="interest" value="看书">看书<br>
        E—mail:<input name="email" type="text" id="PWD224" size="50"><br>

        <input name = "Submit" type = "button"   value = "保存" onclick = check()>
        <input name = "Reset" type = "reset" value = "重新填写">
</form>
</body>
</html>
运行截图:

在这里插入图片描述

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