How do I call a PHP function using AJAX, and get the returned value?

Question

I want to call a specific function from my database.php file, and get the returned value. Here I am trying to do this:

js:

function submit_verification_code(){
$.ajax({
url: "database.php",
type: "post",
data: ({
    'code': code_entered,
}),
dataType:"text",
context: this,
success : function(response) {
    console.log('RESPONSE: ' + response);
    //OPTIONAL_FUNCTION_TO_DO_SOMETHING_WITH_THE_RESPONSE(response);
},
error: function(jqXHR,textStatus,errorThrown){
    //OPTIONAL_FUNCTION_TO_DO_SOMETHING_WITH_THE_ERROR(jqXHR);
    console.log(errorThrown);
}
});
}

database.php

 if(isset($_POST['code'])){
    does_code_match($_POST['code']);
 }
 function does_code_match($code){

    connect();
            die('test');
    $sql = 'select * from emailstobeverified where email=';
    $sql .= "'" . $_SESSION['email'] . "'";
    $sql .= ' and verification_code=';
    $sql .= $code;
    $sql .= ';';
    $count = query($sql)->num_rows;

    die(strval($count));
    disconnect();
    echo strval($count);
    exit;
    //Once you've outputted, make sure nothing else happens
 }

does_code_match function executes, and the console log prints <br /> when console.log("RESPONSE" + response) is called. But I want it to print the value of $count

EDIT:

There is a problem with connect() function. If I call die('test') just before calling connect() , it returns a response! It says "hello world" in the console. If I call it directly AFTER calling connect() , it prints this:

<b>Warning</b>:  Use of undefined constant conn - assumed 'conn' (this will throw an Error in a future version of PHP) in <b>C:\xampp2\htdocs\database.php</b> on line <b>72</b><br />
<br />
<b>Warning</b>:  Use of undefined constant dbhost - assumed 'dbhost' (this will throw an Error in a future version of PHP) in <b>C:\xampp2\htdocs\database.php</b> on line <b>72</b><br />
<br />
<b>Warning</b>:  Use of undefined constant dbuser - assumed 'dbuser' (this will throw an Error in a future version of PHP) in <b>C:\xampp2\htdocs\database.php</b> on line <b>72</b><br />
<br />
<b>Warning</b>:  Use of undefined constant dbpass - assumed 'dbpass' (this will throw an Error in a future version of PHP) in <b>C:\xampp2\htdocs\database.php</b> on line <b>72</b><br />
<br />
<b>Warning</b>:  Use of undefined constant db - assumed 'db' (this will throw an Error in a future version of PHP) in <b>C:\xampp2\htdocs\database.php</b> on line <b>72</b><br />
test

and the response is <br />

Connect function:

 $dbhost = "localhost";
 $dbuser = "root";
 $dbpass = "";
 $db = "example";
 $conn;
 function connect(){
    $GLOBALS[conn] = new mysqli($GLOBALS[dbhost], $GLOBALS[dbuser], $GLOBALS[dbpass],$GLOBALS[db]) or die("Connect failed: %s\n". $GLOBALS[conn] -> error);
 }

Answer 1

Change your jQuery to the following:

$.ajax({
    url: "database.php",
    type: "post",
    dataType: "json",
    data: ({
        code: code_entered,
    }),
    context: this,
    success : function(response) {
        console.log(response);
        //OPTIONAL_FUNCTION_TO_DO_SOMETHING_WITH_THE_RESPONSE(response);
    },
    error: function(jqXHR,textStatus,errorThrown){
        console.log(jqXHR);
        //OPTIONAL_FUNCTION_TO_DO_SOMETHING_WITH_THE_ERROR(jqXHR);
    }
});

Then change your PHP to the following:

 if(isset($_POST['code'])){
    does_code_match($_POST['code']);
    //no need to call echo again
 }

 function does_code_match($code){
     connect();
    $sql = 'select * from emailstobeverified where email=';
    $sql .= "'" . $_SESSION['email'] . "'";
    $sql .= ' and verification_code=';
    $sql .= $code;
    $sql .= ';';
    error_log('Adding code to be verified with query: ' . $sql);
    $count = query($sql)->num_rows;
    disconnect();
    //I can't speak for the above code, I'm assuming it works.

    error_log("CODE MATCHES? "  . $count);
    error_log(json_encode($count));
    //Not sure why you're doing this, but I assume it's for testing only

    echo json_encode($count);
    exit;
    //Once you've outputted, make sure nothing else happens
 }

What kind of stuff do you see in your console.log(response); output? Once you start developing your environment, you will probably start to send back an array of responses instead of just a value.

Answer 2

just echo $count

$count = query($sql)->num_rows;
disconnect();
echo $count;

If you encode the count, on the receiving end, you will have to decode the json first.

Answer 3

When referencing array keys, you must enclose them in quotes, change your function to the following:

function connect(){
    $GLOBALS['conn'] = new mysqli($GLOBALS['dbhost'], $GLOBALS['dbuser'], $GLOBALS['dbpass'],$GLOBALS['db']) or die("Connect failed: %s\n". $GLOBALS['conn'] -> error);
 }

Also, in general, this is a strange way of storing global variables, you should look into using the $_ENV array instead.