wp.media.query() works in the console, but not when run like this in a plugin. halp?

wp.media.query.php

<?php
/*
 * Plugin Name: wp.media.query
 * Plugin URI: trepmal.com
 * Description:
 * Version: 0
 * Author: Kailey Lampert
 * Author URI: kaileylampert.com
 * License: GPLv2 or later
 * TextDomain:
 * DomainPath:
 * Network:
 */

$wpmediaquery_test = new wpmediaquery_test();

class wpmediaquery_test {

	function __construct() {
		add_action( 'add_meta_boxes', array( &$this, 'add_meta_boxes' ) );
	}

	function add_meta_boxes() {
		add_meta_box( 'wpmediaquery-test', 'wp.media.query test', array( &$this, 'add_meta_box' ), 'page', 'normal', 'low');
	}

	function add_meta_box( $post ) {
		echo 'lorem';
		add_action('admin_print_footer_scripts', array( &$this, 'js' ), 99 );
	}

	function js() {
		?><script>
jQuery(document).ready(function($){

	var query = wp.media.query(); // { post__in: [1709] }
	query.more();
	result = query.length;

	console.log( 'query length', result ); // 0

	var singleimage = wp.media.model.Attachment.get( 7 ); // where 7 is the id of a single attachment
	singleimage.fetch();
	result = singleimage.toJSON();

	console.log( 'single img object', result ); // { id: 7 }

});
		</script><?php
	}

}

Can you post the answer?
I also want to query images from the DB and I get an empty object in the console (I'm not that good to know how to use it, and chrome has fooled me before by showing me output in the console different than what JS retrieves)
Thanks.