以下 javacript 用于验证检查。然而警报 当缺少输入时,语句不会出现。 我尝试删除 if 语句并仅使用alert 语句和 脚本工作正常。 if 语句有什么问题吗? 下面是我的 HTML 代码:
<html>
<head>
<title>A More Complex Form with JavaScript Validation</title>
<script type="text/javascript">
// Validation form
function validate_form()
{
valid = true;
// check for missing name
if ( document.contact_form.contact_name.value == "" )
{
alert("Please fill in the 'Your Name' box,");
valid = false;
}
// check for missing gender
if ( document.contact_form.gender[0].checked == false ) && (
document.contact_form.gender[1].checked == false )
{
alert("Please choose your Gender: Male or Female");
valid = false;
}
// check for missing age
if ( document.contact_form.age.selectedIndex == 0 )
{
alert("Please select your Age.");
valid = false;
}
// check for missing terms
if ( document.contact_form.terms == false )
{
alert("Please check the Terms & Conditions box.");
valid = false;
}
return valid;
}
//-->
</script>
</head>
<body>
<h1>Please Enter Your Details Below</h1>
<form name="contact_form" onsubmit="validate_form()">
<p>Your Name:
<input type="text" name="contact_name" size="20">
</p>
<p>
Your Gender:
<input type="radio" name="gender" value="male">Male
<input type="radio" name="gender" value="female">Female
</p>
<p>
Your Age:
<select name="age">
<option value="1">0-14 years</option>
<option value="2">15-30 years</option>
<option value="3">31-44 years</option>
<option value="4">45-60 years</option>
<option value="5">61-74 years</option>
<option value="6">75-90 years</option>
</select>
</p>
<p>
Do you agree to the Terms and Conditions?
<input type="checkbox" name="terms" value="yes">Yes
</p>
<input type="submit" name="submit" value="Send Details">
</form>
</body>
</html>
最佳答案
if ( document.contact_form.gender[0].checked == false ) && (
document.contact_form.gender[1].checked == false )
{
alert("Please choose your Gender: Male or Female");
valid = false;
}
你必须改变这样的条件
if ( document.contact_form.gender[0].checked == false &&
document.contact_form.gender[1].checked == false )
{
alert("Please choose your Gender: Male or Female");
valid = false;
}
由于此错误,您的脚本无法启动。
提示:您可以从 Chrome 控制台等浏览器的开发控制台检查脚本错误。
正如注释中所说的“trincot”,您还可以使用 !
运算符来检查 boolean
值。
if ( !document.contact_form.gender[0].checked && !document.contact_form.gender[1].checked )
{
alert("Please choose your Gender: Male or Female");
valid = false;
}
关于javascript - javascript 中的警报语句不显示?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/43228162/