# Yahoo! UI Library

### yui 3.0.0b1

Yahoo! UI Library > yui > Loader
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## Class Loader

Loader dynamically loads script and css files. It includes the dependency info for the version of the library in use, and will automatically pull in dependencies for the modules requested. It supports rollup files and will automatically use these when appropriate in order to minimize the number of http connections required to load all of the dependencies. It can load the files from the Yahoo! CDN, and it can utilize the combo service provided on this network to reduce the number of http connections required to download YUI files.

### Constructor

Loader `( o )`

Parameters:
  `o <object>` an optional set of configuration options. Valid options:
  - base: The base dir
  - secureBase: The secure base dir (not implemented)
  - comboBase: The YUI combo service base dir. Ex: http://yui.yahooapis.com/combo?
  - root: The root path to prepend to module names for the combo service. Ex: 2.5.2/build/
  - filter: A filter to apply to result urls. This filter will modify the default path for all modules. The default path for the YUI library is the minified version of the files (e.g., event-min.js). The filter property can be a predefined filter or a custom filter. The valid predefined filters are:
    DEBUG
      Selects the debug versions of the library (e.g., event-debug.js). This option will automatically include the Logger widget
    RAW
      Selects the non-minified version of the library (e.g., event.js).
    You can also define a custom filter, which must be an object literal containing a search expression and a replace string:

        myFilter: {
        'searchExp': "-min\\.js",
        'replaceStr': "-debug.js"
        }

  - filters: per-component filter specification. If specified for a given component, this overrides the filter config
  - combine: Use the YUI combo service to reduce the number of http connections required to load your dependencies
  - ignore: A list of modules that should never be dynamically loaded
  - force: A list of modules that should always be loaded when required, even if already present on the page
  - insertBefore: Node or id for a node that should be used as the insertion point for new nodes
  - charset: charset for dynamic nodes (deprecated, use jsAttributes or cssAttributes)
  - jsAttributes: object literal containing attributes to add to script nodes
  - cssAttributes: object literal containing attributes to add to link nodes
  - timeout: number of milliseconds before a timeout occurs when dynamically loading nodes. in not set, there is no timeout
  - context: execution context for all callbacks
  - onSuccess: callback for the 'success' event
  - onFailure: callback for the 'failure' event
  - onCSS: callback for the 'CSSComplete' event. When loading YUI components with CSS the CSS is loaded first, then the script. This provides a moment you can tie into to improve the presentation of the page while the script is loading.
  - onTimeout: callback for the 'timeout' event
  - onProgress: callback executed each time a script or css file is loaded
  - modules: A list of module definitions. See Loader.addModule for the supported module metadata

### Properties

#### _internalCallback - `private object`

Internal callback to handle multiple internal insert() calls so that css is inserted prior to js

#### _useYahooListener - `private object`

Use the YUI environment listener to detect script load. This is only switched on for Safari 2.x and below.

#### allowRollup - `boolean`

Should we allow rollups
Default Value: true

#### attaching - `object`

A list of modules to attach to the YUI instance when complete. If not supplied, the sorted list of dependencies are applied.

#### base - `string`

The base directory.
Default Value: http://yui.yahooapis.com/[YUI VERSION]/build/

#### charset - `string`

The charset attribute for inserted nodes
Deprecated: , use cssAttributes or jsAttributes

#### combine - `boolean`

If configured, YUI JS resources will use the combo handler
Default Value: true if a base dir isn't in the config

#### comboBase - `string`

Base path for the combo service
Default Value: http://yui.yahooapis.com/combo?

#### context - `object`

The execution context for all callbacks
Default Value: {YUI} the YUI instance

#### cssAttributes - `object`

An object literal containing attributes to add to link nodes

#### data - `object`

Data that is passed to all callbacks

#### dirty - `boolean`

Flag to indicate the dependency tree needs to be recomputed if insert is called again.
Default Value: true

#### filter - `string|{searchExp: string, replaceStr: string}`

A filter to apply to result urls. This filter will modify the default path for all modules. The default path for the YUI library is the minified version of the files (e.g., event-min.js). The filter property can be a predefined filter or a custom filter. The valid predefined filters are:

DEBUG
  Selects the debug versions of the library (e.g., event-debug.js). This option will automatically include the Logger widget
RAW
  Selects the non-minified version of the library (e.g., event.js).

You can also define a custom filter, which must be an object literal containing a search expression and a replace string:

    myFilter: {
    'searchExp': "-min\\.js",
    'replaceStr': "-debug.js"
    }

#### filters - `object`

per-component filter specification. If specified for a given component, this overrides the filter config.

#### force - `string[]`

A list of modules that should always be loaded, even if they have already been inserted into the page.

#### ignore - `string[]`

A list of modules that should not be loaded, even if they turn up in the dependency tree

#### ignoreRegistered - `object`

Ignore modules registered on the YUI global
Default Value: false

#### insertBefore - `string|HTMLElement`

Node reference or id where new nodes should be inserted before

#### inserted - `{string: boolean}`

List of modules inserted by the utility

#### jsAttributes - `object`

An object literal containing attributes to add to script nodes

#### loaded - `{string: boolean}`

Set when beginning to compute the dependency tree. Composed of what YUI reports to be loaded combined with what has been loaded by any instance on the page with the version number specified in the metadata.

#### loadOptional - `boolean`

Whether or not to load optional dependencies for the requested modules
Default Value: false

#### moduleInfo - `object`

The library metadata

#### required - `{string: boolean}`

The list of requested modules

#### rollups - `object`

List of rollup files found in the library metadata

#### root - `string`

Root path to prepend to module path for the combo service
Default Value: [YUI VERSION]/build/

#### skin - `object`

Provides the information used to skin the skinnable components. The following skin definition would result in 'skin1' and 'skin2' being loaded for calendar (if calendar was requested), and 'sam' for all other skinnable components: `skin: { // The default skin, which is automatically applied if not // overriden by a component-specific skin definition. // Change this in to apply a different skin globally defaultSkin: 'sam', // This is combined with the loader base property to get // the default root directory for a skin. ex: // http://yui.yahooapis.com/2.3.0/build/assets/skins/sam/ base: 'assets/skins/', // The name of the rollup css file for the skin path: 'skin.css', // The number of skinnable components requested that are // required before using the rollup file rather than the // individual component css files rollup: 3, // Any component-specific overrides can be specified here, // making it possible to load different skins for different // components. It is possible to load more than one skin // for a given component as well. overrides: { calendar: ['skin1', 'skin2'] } }`

#### skipped - `object`

List of skipped modules during insert() because the module was not defined

#### sorted - `string[]`

All of the derived dependencies in sorted order, which will be populated when either calculate() or insert() is called

#### timeout - `int`

Timeout value in milliseconds. If set, this value will be used by the get utility. the timeout event will fire if a timeout occurs.

### Methods

#### _addSkin

`private string _addSkin ( skin , mod , parent )`
Adds the skin def to the module info

Parameters:
  `skin <string>` the name of the skin
  `mod <string>` the name of the module
  `parent <string>` parent module if this is a skin of a submodule or plugin

Returns: `string`
  the module name for the skin

#### _explode

`private void _explode ( )`
Inspects the required modules list looking for additional dependencies. Expands the required list to include all required modules. Called by calculate()

Returns: `void`

#### _filter

`private string _filter ( u , name )`
Apply filter defined for this instance to a url/path method _filter

Parameters:
  `u <string>` the string to filter
  `name <string>` the name of the module, if we are processing a single module as opposed to a combined url

Returns: `string`
  the filtered string

#### _reduce

`private void _reduce ( )`
Remove superceded modules and loaded modules. Called by calculate() after we have the mega list of all dependencies

Returns: `void`

#### _rollup

`private void _rollup ( )`
Look for rollup packages to determine if all of the modules a rollup supersedes are required. If so, include the rollup to help reduce the total number of connections required. Called by calculate()

Returns: `void`

#### _setup

`private void _setup ( )`
Investigates the current YUI configuration on the page. By default, modules already detected will not be loaded again unless a force option is encountered. Called by calculate()

Returns: `void`

#### _sort

`private void _sort ( )`
Sorts the dependency tree. The last step of calculate()

Returns: `void`

#### _url

`private string _url ( path )`
Generates the full url for a module method _url

Parameters:
  `path <string>` the path fragment

Returns: `string`
  the full url

#### addModule

`boolean addModule ( o , name )`
Add a new module to the component metadata.

name:
  required, the component name
type:
  required, the component type (js or css)
path:
  required, the path to the script from "base"
requires:
  array of modules required by this component
optional:
  array of optional modules for this component
supersedes:
  array of the modules this component replaces
after:
  array of modules the components which, if present, should be sorted above this one
rollup:
  the number of superseded modules required for automatic rollup
fullpath:
  If fullpath is specified, this is used instead of the configured base + path
skinnable:
  flag to determine if skin assets should automatically be pulled in
submodules:
  a has of submodules

Parameters:
  `o <object>` An object containing the module data
  `name <object>` the module name (optional), required if not in the module data

Returns: `boolean`
  true if the module was added, false if the object passed in did not provide all required attributes

#### calculate

`void calculate ( o )`
Calculates the dependency tree, the result is stored in the sorted property

Parameters:
  `o <object>` optional options object

Returns: `void`

#### formatSkin

`string formatSkin ( skin , mod )`
Returns the skin module name for the specified skin name. If a module name is supplied, the returned skin module name is specific to the module passed in.

Parameters:
  `skin <string>` the name of the skin
  `mod <string>` optional: the name of a module to skin

Returns: `string`
  the full skin module name

#### getProvides

`getProvides ( name , notMe )`
Returns an object literal of the modules the supplied module satisfies

Parameters:
  `name <string>` The name of the module
  `notMe <string>` don't add this module name, only include superseded modules

#### getRequires

`void getRequires ( mod )`
Returns an object containing properties for all modules required in order to load the requested module

Parameters:
  `mod <object>` The module definition from moduleInfo

Returns: `void`

#### insert

`void insert ( o , type )`
inserts the requested modules and their dependencies. `type` can be "js" or "css". Both script and css are inserted if type is not provided.

Parameters:
  `o <object>` optional options object
  `type <string>` the type of dependency to insert

Returns: `void`

#### loadNext

`void loadNext ( mname )`
Executed every time a module is loaded, and if we are in a load cycle, we attempt to load the next script. Public so that it is possible to call this if using a method other than Y.register to determine when scripts are fully loaded

Parameters:
  `mname <string>` optional the name of the module that has been loaded (which is usually why it is time to load the next one)

Returns: `void`

#### onCSS

`void onCSS ( )`
Callback for the 'CSSComplete' event. When loading YUI components with CSS the CSS is loaded first, then the script. This provides a moment you can tie into to improve the presentation of the page while the script is loading.

Returns: `void`

#### onFailure

`void onFailure ( )`
Callback that will be executed if there is a failure

Returns: `void`

#### onProgress

`void onProgress ( )`
Callback executed each time a script or css file is loaded

Returns: `void`

#### onSuccess

`void onSuccess ( )`
Callback that will be executed when the loader is finished with an insert

Returns: `void`

#### onTimeout

`void onTimeout ( )`
Callback that will be executed if a timeout occurs

Returns: `void`

#### require

`void require ( what )`
Add a requirement for one or more module

Parameters:
  `what <string[] | string*>` the modules to load

Returns: `void`

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