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Loader Class

Ext.Loader is the heart of the new dynamic dependency loading capability in Ext JS 4+. It is most commonly used via the Ext.require shorthand. Ext.Loader supports both asynchronous and synchronous loading approaches, and leverage their advantages for the best development flow. We'll discuss about the pros and cons of each approach:

Asynchronous Loading

  • Advantages:

    • Cross-domain
    • No web server needed: you can run the application via the file system protocol (i.e:
    • Best possible debugging experience: error messages come with the exact file name and line number
  • Disadvantages:

    • Dependencies need to be specified before-hand

Method 1: Explicitly include what you need:

// Syntax
            Ext.require({String/Array} expressions);
            // Example: Single alias
            // Example: Single class name
            // Example: Multiple aliases / class names mix
            Ext.require(['widget.window', 'layout.border', '']);
            // Wildcards
            Ext.require(['widget.*', 'layout.*', '*']);

Method 2: Explicitly exclude what you don't need:

// Syntax: Note that it must be in this chaining format.
            Ext.exclude({String/Array} expressions)
            .require({String/Array} expressions);
            // Include everything except*
            // Include all widgets except widget.checkbox*,
            // which will match widget.checkbox, widget.checkboxfield, widget.checkboxgroup, etc.

Synchronous Loading on Demand

  • Advantages:

    • There's no need to specify dependencies before-hand, which is always the convenience of including ext-all.js before
  • Disadvantages:

    • Not as good debugging experience since file name won't be shown (except in Firebug at the moment)
    • Must be from the same domain due to XHR restriction
    • Need a web server, same reason as above

There's one simple rule to follow: Instantiate everything with Ext.create instead of the new keyword

    Ext.create('widget.window', { ... }); // Instead of new Ext.window.Window({...});
            Ext.create('Ext.window.Window', {}); // Same as above, using full class name instead of alias
            Ext.widget('window', {}); // Same as above, all you need is the traditional `xtype`

Behind the scene, Ext.ClassManager will automatically check whether the given class name / alias has already existed on the page. If it's not, Ext.Loader will immediately switch itself to synchronous mode and automatic load the given class and all its dependencies.

Hybrid Loading - The Best of Both Worlds

It has all the advantages combined from asynchronous and synchronous loading. The development flow is simple:

Step 1: Start writing your application using synchronous approach.

Ext.Loader will automatically fetch all dependencies on demand as they're needed during run-time. For example:

            var window = Ext.widget('window', {
            width: 500,
            height: 300,
            layout: {
            type: 'border',
            padding: 5
            title: 'Hello Dialog',
            items: [{
            title: 'Navigation',
            collapsible: true,
            region: 'west',
            width: 200,
            html: 'Hello',
            split: true
            }, {
            title: 'TabPanel',
            region: 'center'

Step 2: Along the way, when you need better debugging ability, watch the console for warnings like these:

[Ext.Loader] Synchronously loading 'Ext.window.Window'; consider adding Ext.require('Ext.window.Window') before your application's code
            [Ext.Loader] Synchronously loading 'Ext.layout.container.Border'; consider adding Ext.require('Ext.layout.container.Border') before your application's code

Simply copy and paste the suggested code above Ext.onReady, i.e:


Everything should now load via asynchronous mode.


It's important to note that dynamic loading should only be used during development on your local machines. During production, all dependencies should be combined into one single JavaScript file. Ext.Loader makes the whole process of transitioning from / to between development / maintenance and production as easy as possible. Internally Ext.Loader.history maintains the list of all dependencies your application needs in the exact loading sequence. It's as simple as concatenating all files in this array into one, then include it on top of your application.

This process will be automated with Sencha Command, to be released and documented towards Ext JS 4 Final.

Namespace: Ext

Base Types




Name Description
disableCaching Appends current timestamp to script files to prevent caching. Defaults to: true
disableCachingParam The get parameter name for the cache buster's timestamp. Defaults to: "_dc"
enabled Whether or not to enable the dynamic dependency loading feature. Defaults to: false
garbageCollect True to prepare an asynchronous script tag for garbage collection (effective only if preserveScripts is false) Defaults to: false
paths The mapping from namespaces to file paths
            'Ext': '.', // This is set by default, Ext.layout.container.Container will be
            // loaded from ./layout/Container.js
            'My': './src/my_own_folder' // My.layout.Container will be loaded from
            // ./src/my_own_folder/layout/Container.js
Note that all relative paths are relative to the current HTML document. If not being specified, for example, Other.awesome.Class will simply be loaded from ./Other/awesome/Class.js Defaults to: {"Ext": "."}
preserveScripts False to remove and optionally garbage-collect asynchronously loaded scripts, True to retain script element for browser debugger compatibility and improved load performance. Defaults to: true
scriptChainDelay millisecond delay between asynchronous script injection (prevents stack overflow on some user agents) 'false' disables delay but potentially increases stack load. Defaults to: false
scriptCharset Optional charset to specify encoding of dynamic script content.


Name Description
exclude(JsArray) Explicitly exclude files from being loaded. Useful when used in conjunction with a broad include expression. Can be chained with more require and exclude methods, eg:
getConfig(JsString) Get the config value corresponding to the specified name. If no name is given, will return the config object
getPath(JsString) Translates a className to a file path by adding the the proper prefix and converting the .'s to /'s. For example:
  Ext.Loader.setPath('My', '/path/to/My');
            alert(Ext.Loader.getPath('My.awesome.Class')); // alerts '/path/to/My/awesome/Class.js'
Note that the deeper namespace levels, if explicitly set, are always resolved first. For example:
            'My': '/path/to/lib',
            'My.awesome': '/other/path/for/awesome/stuff',
            'My.awesome.more': '/more/awesome/path'
            alert(Ext.Loader.getPath('My.awesome.Class')); // alerts '/other/path/for/awesome/stuff/Class.js'
            alert(Ext.Loader.getPath('My.awesome.more.Class')); // alerts '/more/awesome/path/Class.js'
            alert(Ext.Loader.getPath('')); // alerts '/path/to/lib/cool/Class.js'
            alert(Ext.Loader.getPath('Unknown.strange.Stuff')); // alerts 'Unknown/strange/Stuff.js'
loadScript(object) Loads the specified script URL and calls the supplied callbacks. If this method is called before Ext.isReady, the script's load will delay the transition to ready. This can be used to load arbitrary scripts that may contain further Ext.require calls.
onReady(Delegate, object, bool) Add a new listener to be executed when all required scripts are fully loaded
require(object, Delegate, object, object) Loads all classes by the given names and all their direct dependencies; optionally executes the given callback function when finishes, within the optional scope. This method is aliased by Ext.require for convenience
setConfig(object) Set the configuration for the loader. This should be called right after ext-(debug).js is included in the page, and before Ext.onReady. i.e:
<script type="text/javascript" src="ext-core-debug.js"></script>
            <script type="text/javascript">
            enabled: true,
            paths: {
            'My': 'my_own_path'
            <script type="text/javascript">
            Ext.onReady(function() {
            // application code here
Refer to config options of Ext.Loader for the list of possible properties
setPath(object, JsString) Sets the path of a namespace. For Example:
  Ext.Loader.setPath('Ext', '.');
syncRequire(object, Delegate, object, object) Synchronously loads all classes by the given names and all their direct dependencies; optionally executes the given callback function when finishes, within the optional scope. This method is aliased by Ext.syncRequire for convenience


Name Description
history An array of class names to keep track of the dependency loading order. This is not guaranteed to be the same everytime due to the asynchronous nature of the Loader.
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