如何访问if语句中的变量

Question

I have a registation form where I check with AJAX response onkeyup if the username or email allready exists in my database.

You can see how I check it here:

$query = $_GET ['query'];
$field = $_GET ['field'];

if ($field == "username")
    {
        $check = $db->prepare("SELECT * FROM users WHERE username = :query");
        $check->bindParam(':query', $query);
        $check->execute();
        $count = $check->rowCount();

        if ($count > 0)
        {
            echo '<font color=red>Username already exists</font>';
        }
        else 
        {
            echo '<font color=green>Username avalable</font>';
        }
    }

if ($field == "email") 
    {
        $check = $db->prepare("SELECT * FROM users WHERE email = :query");
        $check->bindParam(':query', $query);
        $check->execute();
        $count2 = $check->rowCount();

        if ($count2 > 0)
        {
            echo '<font color=red>Email already exists</font>';
        }
        else 
        {
            echo '<font color=green>Email avalable</font>';
        }   

        if (!filter_var($query, FILTER_VALIDATE_EMAIL)) {
            echo '<font color=red><br />Please enter a valid Email</font>';
        }
        else {
            echo '<font color=green><br />Valid email</font>';
        }
    }

I want to create another if statement where, if there are any errors, then it should disable the submit button. I don't wanna add the disable to each of the statements I already have, cause then I could end with a situation like this:

I enter an email that exists and it disables the submit button. I then enter a correct username and it enables the submit button again, even though the email is still wrong.

So I wan't to create something like this:

if ($count > 0 || $count2 > 0)
{
echo '<script id="cb" type="text/javascript">document.getElementById("regr_btn").disabled=true</script>'
}
else
{
echo '<script id="cb" type="text/javascript">document.getElementById("regr_btn").disabled=false</script>'
}

But I cannot acess my counts since they are not global. Can any of you give me an idea on how I could accomplish this?

Don't worry. I'm also checking for errors when the form is submitted. I know that a user can easily activate the submit button themselves.

Also, please let me know if I need to provide more of my code.

Edit:

Validation function:

<script type='text/javascript'>
            function validate(field, query)
            {
                xmlhttp = new XMLHttpRequest(); // Creating Object
                xmlhttp.onreadystatechange = function() // Checking if readyState changes
                {
                    if (xmlhttp.readyState!=4 && xmlhttp.status==200) // Validation Under Process 
                    {
                        document.getElementById(field).innerHTML = "Validating..";
                    }
                    else if (xmlhttp.readyState==4 && xmlhttp.status==200)  // Validation Completed
                    {
                        document.getElementById(field).innerHTML = xmlhttp.responseText;
                    }
                    else // If an error is encountered
                    {
                        document.getElementById(field).innerHTML = "Unknown Error Occurred. <a href='index.php'>Reload</a> the page.";
                    }
                }
                xmlhttp.open("GET","check.php?field="+field+"&query="+query, false);
                xmlhttp.send();
            }
        </script>

And the code in the first codeblock is inside the check.php file

Email and username fields in my form:

<div id='username'></div>
<input type="email" name="email" placeholder="Email" required="required" onkeyup="validate('email', this.value)"><br>
<div id='email'></div>
<input type="password" name="password" placeholder="Password" required="required" onkeyup="validate('password', this.value)"><br>

Answer 1

DO this:

$query = $_GET ['query'];
$field = $_GET ['field'];
// Set counter to 0
$count = 0;
// Store all messages here
$msg = "";

if ($field == "username")
    {
        $check = $db->prepare("SELECT * FROM users WHERE username = :query");
        $check->bindParam(':query', $query);
        $check->execute();

        if ($check->rowCount() > 0)
        {
            $count += 1;
            $msg = '<font color=red>Username already exists</font>';
        }
        else 
        {
            $msg = '<font color=green>Username avalable</font>';
        }
    }

if ($field == "email") 
    {
        $check = $db->prepare("SELECT * FROM users WHERE email = :query");
        $check->bindParam(':query', $query);
        $check->execute();

        if ($check->rowCount() > 0)
        {
            $count += 1;
            $msg .= '<br /><font color=red>Email already exists</font>';
        }
        else 
        {
            $msg .= '<br /><font color=green>Email avalable</font>';
        }   

        if (!filter_var($query, FILTER_VALIDATE_EMAIL)) {
            $msg .= '<font color=red><br />Please enter a valid Email</font>';
        }
        else {
            $msg .= '<font color=green><br />Valid email</font>';
        }
    }

if ($count > 0)
{
  // Disable submit button here
  // Alternatively you can add the javascript that disables the submit button to
  // The $msg like so: $msg .= "<script></script>"; and echo it all together.
}
echo $msg;