Javascript Validation for email(正则表达式) 英文翻译

Try testing the following form with valid and invalid email addresses. The
code uses javascript to match the users input with a regular expression.
函数代码：

function validate(form_id,email) { 
var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/; 
var address = document.forms[form_id].elements[email].value; 
if(reg.test(address) == false) { 
alert('Invalid Email Address'); 
return false; 
} 
}

In the forms ‘onsubmit' code call javascript:return validate(‘form_id','email_field_id')
使用方法：

<form id="form_id" method="post" action="action.php" onsubmit="javascript:return validate('form_id','email');"> 
<input type="text" id="email" name="email" /> 
<input type="submit" value="Submit" /> 
</form>

You should not rely purely on client side validation on your website / web application, if the user has javascript disabled this will not work. Always validate on the server.
from:　http://www.white-hat-web-design.co.uk/blog/javascript-validation/