Calling PHP functions in Javascript using AJAX

ajax, javascript, php

Solution

You can't call a function in PHP directly - but you can call a PHP page that in turn can call the PHP function. For example...

service.php

include_once('something.php');
$model = new Something_Model();
$model->check_availability();

something.js

function check_availability() {

    var request = new XMLHttpRequest();
    request.open('GET', 'http://yoursite/service.php', false);
    request.send();

    if (request.status === 200) {
      alert(request.responseText);
    }
}

I have used a really simple example of an XMLHttpRequest - this example actually blocks while the request is made. In reality you may want to use a callback and allow it to run asynchronously but I wanted to keep the answer as short as possible.

Problem

I have a javascript file and I want to call a function on the php server side and return the result back to the client side using ajax, but I am not sure how to make the request to the specific php function. Here are my files: The javascript file basically retrieves the username from the html form, and I want to send that username to php and check against the database for availability. In `something.js`: ``` function check_availability() { var username = $.trim(document.getElementById('usernameField').value); var xmlhttp= new XMLHttpRequest(); // not sure how to make the request here to check_availability() under php } ``` The PHP file will just check the username thats being passed from the js file against the database, if its available return true, else false. In `something.php`: ``` class Something_Model { private $data; private $table; public function __construct() { $this->data = new udata(DBSERVER, DBUSERNAME, DBPASSWORD, DBNAME); } # check for username availability public function check_availability() { // make the check here, but needs to retrieve username from js file echo "here"; } } ``` So, inside the Something_Model class, I want to make the check_availability() call from javascript, can someone give me an example to make this ajax call? Also, how do I return the result back to the javascript? Do I need to encode it as a JSON obj? Thanks a lot.

Original source