“Add Media” button in custom plugin

If you want to add a add media button to your admin panels:

You need to use wp_enqueue_media();

add_action ( 'admin_enqueue_scripts', function () {
    if (is_admin ())
        wp_enqueue_media ();
} );

Then use this js:

jQuery(document).ready(function() {
    var $ = jQuery;
    if ($('.set_custom_images').length > 0) {
        if ( typeof wp !== 'undefined' && wp.media && wp.media.editor) {
            $('.set_custom_images').on('click', function(e) {
                e.preventDefault();
                var button = $(this);
                var id = button.prev();
                wp.media.editor.send.attachment = function(props, attachment) {
                    id.val(attachment.id);
                };
                wp.media.editor.open(button);
                return false;
            });
        }
    }
});

Use this html:

<p>
    <input type="number" value="" class="regular-text process_custom_images" id="process_custom_images" name="" max="" min="1" step="1">
    <button class="set_custom_images button">Set Image ID</button>
</p>