admin-ajax.php vs Custom Page Template for Ajax Requests

Question

Is there any reason to use admin-ajax.php for ajax requests versus a custom page template?

I didn't know about admin-ajax.php until recently, so what I had been doing is creating a custom page template like this:

<?php
/**
 * Template Name: API
 */

if ( isset( $_GET['ajax_request'] ) ) {
// do stuff
}

And the ajax call would be to the URL http://mysite.com/api/, which is where I've published a blank page using my API page template. This seems to give me access to all my WordPress functions and spit out data.

However, recently I've read up on admin-ajax.php and understand another way to connect to the WordPress database is to call the URL http://mysite.com/wp-admin/admin-ajax.php and have functions like this:

add_action( 'wp_ajax_nopriv_action', 'my_do_stuff' );
add_action( 'wp_ajax_show_action', 'my_do_stuff' );

function my_do_stuff() {
// do stuff
}

Is it wrong to connect the first way? Does admin-ajax.php provide extra security or something? Thanks any input!

Answer 1

First, the obvious drawback to the first method is that it depends on your specific page, template, and permalink structure to all work correctly. Using admin-ajax.php will work correctly in any context, theme or plugin, where proper WordPress best practices are followed.

The less obvious drawback to the first method is that it uses more memory than doing WordPress-enabled AJAX calls, since the whole WordPress environment is loaded, as it's presumed that a front-end or admin page will be output.

The addition of NONCEs with admin-ajax.php provides easy, built-in security.