Register a general javascript file using the EXAMPLE_JS_URL constant defined in the main plugin file

scripts.php

<?php
/**
* Enqueue a JavaScript file using a constant
* called EXAMPLE_JS_URL to get the plugin's js directory url.
*
* @author FAT Media <http://youneedfat.com>
* @copyright Copyright (c) 2013, FAT Media, LLC
* @license GPL-2.0+
*/

/**
 * Enqueue with hook 'wp_enqueue_scripts', 
 * which can be used for front end CSS and JavaScript
 */
add_action( 'wp_enqueue_scripts', 'example_load_javascript' );

/**
 * Enqueue plugin js-file
 */
function example_load_javascript() {
	// Add a trailing slash to the js url
	$js_url = trailingslashit( EXAMPLE_JS_URL );
	// Enqueue general.js file which depends on jQuery
	wp_enqueue_script( 'example-general', $js_url . 'general.js' , array( 'jquery' ), '1.0', true );
}

A full tutorial on defining and using plugin URLs in a WordPress Must Use plugin can be found at http://youneedfat.com/get-the-mu-plugin-directory-url/