导入

    /**

     * Creates the node for the load command. Only used in browser envs.

     */

    req.createNode = function (config, moduleName, url) {

        var node = config.xhtml ?

                document.createElementNS('http://www.w3.org/1999/xhtml', 'html:script') :

                document.createElement('script');

        node.type = config.scriptType || 'text/javascript';

        node.charset = 'utf-8';

        node.async = true;

        return node;

    };

/**

     * Does the request to load a module for the browser case.

     * Make this a separate function to allow other environments

     * to override it.

     *

     * @param {Object} context the require context to find state.

     * @param {String} moduleName the name of the module.

     * @param {Object} url the URL to the module.

     */

    req.load = function (context, moduleName, url) {

        var config = (context && context.config) || {},

            node;

        if (isBrowser) {

            //In the browser so use a script tag

            node = req.createNode(config, moduleName, url);

            node.setAttribute('data-requirecontext', context.contextName);

            node.setAttribute('data-requiremodule', moduleName);

            //Set up load listener. Test attachEvent first because IE9 has

            //a subtle issue in its addEventListener and script onload firings

            //that do not match the behavior of all other browsers with

            //addEventListener support, which fire the onload event for a

            //script right after the script execution. See:

            //https://connect.microsoft.com/IE/feedback/details/648057/script-onload-event-is-not-fired-immediately-after-script-execution

            //UNFORTUNATELY Opera implements attachEvent but does not follow the script

            //script execution mode.

            if (node.attachEvent &&

                    //Check if node.attachEvent is artificially added by custom script or

                    //natively supported by browser

                    //read https://github.com/jrburke/requirejs/issues/187

                    //if we can NOT find [native code] then it must NOT natively supported.

                    //in IE8, node.attachEvent does not have toString()

                    //Note the test for "[native code" with no closing brace, see:

                    //https://github.com/jrburke/requirejs/issues/273

                    !(node.attachEvent.toString && node.attachEvent.toString().indexOf('[native code') < 0) &&

                    !isOpera) {

                //Probably IE. IE (at least 6-8) do not fire

                //script onload right after executing the script, so

                //we cannot tie the anonymous define call to a name.

                //However, IE reports the script as being in 'interactive'

                //readyState at the time of the define call.

                useInteractive = true;

                node.attachEvent('onreadystatechange', context.onScriptLoad);

                //It would be great to add an error handler here to catch

                //404s in IE9+. However, onreadystatechange will fire before

                //the error handler, so that does not help. If addEventListener

                //is used, then IE will fire error before load, but we cannot

                //use that pathway given the connect.microsoft.com issue

                //mentioned above about not doing the 'script execute,

                //then fire the script load event listener before execute

                //next script' that other browsers do.

                //Best hope: IE10 fixes the issues,

                //and then destroys all installs of IE 6-9.

                //node.attachEvent('onerror', context.onScriptError);

            } else {

                node.addEventListener('load', context.onScriptLoad, false);

                node.addEventListener('error', context.onScriptError, false);

            }

            node.src = url;

            //For some cache cases in IE 6-8, the script executes before the end

            //of the appendChild execution, so to tie an anonymous define

            //call to the module name (which is stored on the node), hold on

            //to a reference to this node, but clear after the DOM insertion.

            currentlyAddingScript = node;

            if (baseElement) {

                head.insertBefore(node, baseElement);

            } else {

                head.appendChild(node);

            }

            currentlyAddingScript = null;

            return node;

        } else if (isWebWorker) {

            try {

                //In a web worker, use importScripts. This is not a very

                //efficient use of importScripts, importScripts will block until

                //its script is downloaded and evaluated. However, if web workers

                //are in play, the expectation that a build has been done so that

                //only one script needs to be loaded anyway. This may need to be

                //reevaluated if other use cases become common.

                importScripts(url);

                //Account for anonymous modules

                context.completeLoad(moduleName);

            } catch (e) {

                context.onError(makeError('importscripts',

                                'importScripts failed for ' +

                                    moduleName + ' at ' + url,

                                e,

                                [moduleName]));

            }

        }

    };