loader.js

gistfile1.txt

/**
 * Loader
 */
(function() {
    
    var cache = {};
    
    /**
     * Initialize loader
     * Looks for init-script tag and starts the loading process
     */
    window.addEventListener('load', function onReady() {
        window.removeEventListener('load', onReady);
        var script = document.querySelector('script[data-src][data-loader]');
        
        loadScript(script.getAttribute('data-src'));
    });
    
    /**
     * Reprents a single file and it's corresponding data
     * @constructor
     * @extends {Promise}
     * @param {string} name
     * @param {Array.<string>} requirements
     * @param {Function} factory
     */
    function Module(name, requirements, factory) {
        
        this.name = name;
        this.path = name + '.js';
        this.requires = requirements;
        
        var self = this;
        Promise.call(this, function(res, rej) {
            var required = requirements.map(require);
            Promise.all(required).then(function(modules) {
                try {
                    res(factory.apply(self, modules));
                } catch (e) {
                    rej(e);
                }
            });
        });
    }
    Module.prototype = Object.create(Promise.prototype);
    Module.prototype.require = require;
    Module.prototype.has = function(name) {
        return !!cache[name];
    };
    
    /**
     * Get a defined script by name 
     * {string} name
     * @return {Promise}
     */
    function require(name) {
        if (cache[name]) return cache[name];
        
        return loadScript(name).then(function() {
            return cache[name];
        });
    }
    
    /**
     * Loads a script asynchronously
     * @param {string} name - unnormalized
     * @return {Promise}
     */
    function loadScript(name) {
        var path = name + '.js';
        
        return new Promise(function(res, rej) {
            var script = document.createElement('script');
            script.type = 'text/javascript';
            script.async = true;
            script.src = path;
            script.setAttribute('data-name', name);
            document.head.appendChild(script);
            
            script.onerror = rej;
            script.onload = res;
        });
    }
    
    //
    // Public functions
    //
    
    var defined = {};
    
    /**
     * Define a class and inject requirements
     */
    window.define = function define(requirements, factory) {
        // TODO check for one define call
        var name = document.currentScript.getAttribute('data-name');
        
        // only allow one define call per path
        if (defined[name]) {
            throw new Error("Object already defined under same path: '" + name + "'");
        } else {
            defined[name] = true;
        }
        
        /**
         * return the module to the define call
         * this lets people handle the resulting promise. e.g.
         *
         * define([], function() {
         *
         * }).catch(function(err) {
         *     document.write('there was an error.');
         * });
         */
        return cache[name] = new Module(name, requirements, factory);
    };
})();