js如何判断邮箱格式是否正确

<form action="#"onsubmit="return validate_form(this);" method="post"> Email: <input type="text" name="email" size="30">
 <input type="submit" value="Submit">
</form>
<script type="text/javascript"> function validate_required(field,alerttxt)
 { with (field)
 { if (value==null||value=="")
 {alert(alerttxt);return false} else {return true}
 }
 } function validate_email(field,alerttxt)
 { with (field)
 { apos=value.indexOf("@") dotpos=value.lastIndexOf(".") if (apos<1||dotpos-apos<2)
 {alert(alerttxt);return false} else {return true}
 }
 } function validate_form(thisform)
 { with (thisform)
 { if (validate_required(email,"请填入内容!")==false)
 {email.focus();return false} if (validate_email(email,"请填写正确的邮箱格式!")==false)
 {email.focus();return false}
 }
 }
</script>