AJAX in WordPress Themes

Backend

Let's add the function that will return the AJAX response from the backend. This is normally added to the theme functions.php file:

add_action( 'wp_ajax_my_ajax_method', 'my_ajax_method' );
add_action( 'wp_ajax_nopriv_my_ajax_method', 'my_ajax_method' );
function my_ajax_method() {
    check_ajax_referer( 'my-nonce', 'nonce' );
    // do something...
    wp_send_json( [ 'success' => true ] );
}

Notes:

• We need to add a second nopriv action so that the request works for users who are not logged in.

• wp_send_json takes care of setting the Content-Type: application/json header and also calls wp_die to prevent any further processing.

Frontend

First, we need to output some variables to use in our frontend Javascript. Again in the theme functions.php file:

wp_localize_script( 'my-handle', 'MyScript', [
    'ajaxurl' => admin_url( 'admin-ajax.php' ),
    'nonce'   => wp_create_nonce( 'my-nonce' ),
] );

Notes:

• my-handle should be the same as the handle for your enqueued script file.

• These variables will be made available as a global Javascript object with the given object name. For example, MyScript.ajaxurl.

• ajaxurl is not defined for the frontend so we'll just add it here.

Finally, we can create the AJAX request on the frontend. Using jQuery, it will look something like this:

$.post( MyScript.ajaxurl, {
    action: 'my_ajax_method',
    nonce: MyScript.nonce,
} )
    .done( function ( response ) {
        // do something...
    } )
    .fail( function ( jqXHR, textStatus, error ) {
        console.error( error );
    } );