Removing jQuery migrate and working with dependencies

First part…

OK, so in your theme/plugin you have:

wp_enqueue_script( 'jquery' );
wp_enqueue_script( 'scripts', get_template_directory_uri() . '/js/scripts.min.js', array( 'jquery' ) );

The first line, enqueuing jquery isn’t necessary – you put jquery as dependency in second line, so it will be included anyway.

These lines inform WP that you want to enqueue given file as scripts and it needs script registered with handle jquery – so it will be enqueued automatically before your script.

And the second part…

add_filter( 'wp_default_scripts', 'remove_jquery_migrate' );

function remove_jquery_migrate( &$scripts){
    if(!is_admin()){
        $scripts->remove( 'jquery');
        $scripts->add( 'jquery', false, array( 'jquery-core' ), '1.2.1' );
    }
}

As you can see in Plugin API/Action Reference, this hook is called pretty early… Waaaaay before wp_enqueue_scripts.

And what it really does?

It removes script with handle jquery from default scripts, and then adds it with different dependencies (only jquery-core).

add method comes from WP_Dependencies class:

WP_Dependencies::add( string $handle, string $src, array $deps = array(), string|bool|null $ver = false, mixed $args = null )

And why that version?

The version 1.2.1 is just a cache booster. WordPress does not analyze it. It is used as ?ver param, so browsers have to reload that file, when the version changes… You can put anything in there – of course using real version of given script is a good idea 😉