jQuery Ajax PHP function call returning [object Object]

Question

I want to reload page using with jQuery Ajax. I have the code below, however, it's not working and is returning error [object Object]

Is this just a simple syntax problem, or is my whole logic problematic? It is working perfectly without Javascript, but I'm thinking the UI is more intuitive with jQuery Ajax.

functions.php

//enqueue scripts
function my_theme_enqueue_scripts() {
     wp_enqueue_script('jquery-ui', 'https://code.jquery.com/ui/1.12.1/jquery-ui.min.js', array('jquery'), '1.12.1');
     wp_register_script( 'myjs', get_stylesheet_directory_uri() . '/my.js', array('jquery'),'1.0.0');
     wp_enqueue_script('myjs');
     wp_localize_script( 'ajax-script', 'admin-ajax', array( 'ajax_url' => admin_url( 'admin-ajax.php' ) ) );
}
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_scripts' );

function load_projectmessages($projectid) {
     global $wpdb;
     $sql_displaymessages = $wpdb->prepare("some sql", $projectid );
     $projectmessages = $wpdb->get_results($sql_displaymessages);
     return $projectmessages;
     wp_die();
}
add_action('wp_ajax_load_projectmessages', 'load_projectmessages');

Page Template PHP:

<form id="form-pm" method="post" enctype="multipart/form-data" action="">
            <table>
                <tr>
                    <td><textarea name="projectMessage" rows=3 id="project-message"></textarea></td>
                </tr>
                <tr>
                    <td><input type="submit" name="send" value="send message"></td>
                </tr>
            </table>
        </form>

my.js

function getUrlVars()
    {
        var vars = [], hash;
        var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
        for(var i = 0; i < hashes.length; i++)
        {
            hash = hashes[i].split('=');

            if($.inArray(hash[0], vars)>-1)
            {
                vars[hash[0]]+=","+hash[1];
            }
            else
            {
                vars.push(hash[0]);
                vars[hash[0]] = hash[1];
            }
        }
        return vars;
    }

    $("#form-pm").submit(function(e) {

        e.preventDefault();
        var pID = getUrlVars()["id"];
        $.ajax({
            url: "admin-ajax.ajax_url",
            type: "POST",
            data: {
                action: "load_projectmessages",
                projectid: pID
            },
            success: function(data) { },
            error: function(errorData) { alert(errorData); }
        });
        return false;
    });

Answer 1

OK, so there are multiple problems with your code...

1. Incorrect localization of script

Here's your function that enqueues and localizes the scripts:

function my_theme_enqueue_scripts() {
     wp_enqueue_script('jquery-ui', 'https://code.jquery.com/ui/1.12.1/jquery-ui.min.js', array('jquery'), '1.12.1');
     wp_register_script( 'myjs', get_stylesheet_directory_uri() . '/my.js', array('jquery'),'1.0.0');
     wp_enqueue_script('myjs');
     wp_localize_script( 'ajax-script', 'admin-ajax', array( 'ajax_url' => admin_url( 'admin-ajax.php' ) ) );
}
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_scripts' );

So you localize script called ajax-script, but there is no such script registered. It should be:

wp_localize_script( 'myjs', 'admin-ajax', array( 'ajax_url' => admin_url( 'admin-ajax.php' ) ) );

2. Incorrect name of variable

In wp_localize_script the second parameter is a name for variable that will be created in JS. You put admin-ajax in there and that isn't a correct name for variable.

Change it to:

wp_localize_script( 'myjs', 'MyJS_Data', array( 'ajax_url' => admin_url( 'admin-ajax.php' ) ) );

3. Incorrect AJAX url in $.ajax call

In my.js file you have:

$("#form-pm").submit(function(e) {

    e.preventDefault();
    var pID = getUrlVars()["id"];
    $.ajax({
        url: "admin-ajax.ajax_url",
        type: "POST",
        data: {

So you pass a string "admin-ajax.ajax_url" string as URL and this isn't a correct url address...

It should be:

url: MyJS_Data.ajax_url,

as you want to use variable, and not a string and we've changed name of that variable in 2...

4. Incorrect usage of AJAX callback function.

In your PHP code you have:

function load_projectmessages($projectid) {
     global $wpdb;
     $sql_displaymessages = $wpdb->prepare("some sql", $projectid );
     $projectmessages = $wpdb->get_results($sql_displaymessages);
     return $projectmessages;
     wp_die();
}
add_action('wp_ajax_load_projectmessages', 'load_projectmessages');

But... This function doesn't print anything, so your AJAX request won't get any result.

On the other hand you do 2 things:

 return $projectmessages;
 wp_die();

So your function will return (not print) $projectmessages. The next line won't be called, because function ends its execution, when you return a value.

So it should be something like this:

function load_projectmessages($projectid) {
     global $wpdb;
     $sql_displaymessages = $wpdb->prepare("some sql", $projectid );
     $projectmessages = $wpdb->get_results($sql_displaymessages);
     echo json_encode( $projectmessages );
     wp_die();
}
add_action('wp_ajax_load_projectmessages', 'load_projectmessages');

This way your function will "return" $projectmessages encoded as JSON.