使用jQuery和PHP检查验证码(Checking captcha with jQuery and PHP)

 我正在编写动态联系表格。 代码如下所示： 
 jQuery的： 
 
$.ajax({
    type: "POST",
    url: "sendmail.php",
    data: {email: email, message: message, captcha: captcha}
})
.done(function( result ) {
    alert(result);
})
 
 PHP： 
 
<?php
    session_start();
    $email = $_POST['email'];
    $message = $_POST['message'];
    $captcha = $_POST['captcha'];

    if(isset($_POST["captcha"])&&$_POST["captcha"]!=""&&strtoupper($_SESSION["captcha_code"])==strtoupper($_POST["captcha"]))
    {
        @mail('mymail@gmail.com', 'Subject', $message, 'From:' . email);
        echo "Message successfully sent.";
    }
    else
    {
        // change opacity of #error div
    }
?>
 
 问题是如果输入了错误的验证码，如何更改隐藏div的不透明度？ 在这种情况下，我需要在PHP脚本或其他地方插入此代码： 
 
$('#error').css({opacity:'1'}); 
 
 请记住，我不能用echo注入代码，因为我使用alert来提供从PHP脚本返回的信息。 

I'm coding dynamic contact form. The code look like this:
 jQuery:
 
$.ajax({
    type: "POST",
    url: "sendmail.php",
    data: {email: email, message: message, captcha: captcha}
})
.done(function( result ) {
    alert(result);
})
 
PHP:
 
<?php
    session_start();
    $email = $_POST['email'];
    $message = $_POST['message'];
    $captcha = $_POST['captcha'];

    if(isset($_POST["captcha"])&&$_POST["captcha"]!=""&&strtoupper($_SESSION["captcha_code"])==strtoupper($_POST["captcha"]))
    {
        @mail('mymail@gmail.com', 'Subject', $message, 'From:' . email);
        echo "Message successfully sent.";
    }
    else
    {
        // change opacity of #error div
    }
?>
 
The problem is how to change opacity of hidden div if wrong captcha code has been entered? In that case I need to insert this code insid PHP script or somewhere else:
 
$('#error').css({opacity:'1'}); 
 
Remember, that I cannot inject code with echo, because I use alert for information coming back from PHP script.

原文：https://stackoverflow.com/questions/17845398