How to add custom javascript to WordPress Admin?

There is a snippet for Your functions.php file :

function custom_admin_js() {
    $url = get_bloginfo('template_directory') . '/js/wp-admin.js';
    echo '"<script type="text/javascript" src="'. $url . '"></script>"';
}
add_action('admin_footer', 'custom_admin_js');

Works fine on Wordpress 3.2.1.

Use the admin_enqueue_scripts action and the wp_enqueue_script method to add custom scripts to the admin interface.

This assumes that you have myscript.js in your plugin folder. Change accordingly. The my_custom_script handle should be unique for your module and script.

function my_enqueue($hook) {
    // Only add to the edit.php admin page.
    // See WP docs.
    if ('edit.php' !== $hook) {
        return;
    }
    wp_enqueue_script('my_custom_script', plugin_dir_url(__FILE__) . '/myscript.js');
}

add_action('admin_enqueue_scripts', 'my_enqueue');