# Yahoo! UI Library

### imageloader 2.8.1

Yahoo! UI Library > imageloader > YAHOO.util.ImageLoader.group
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## Class YAHOO.util.ImageLoader.group

A group for images. A group can have one time limit and a series of triggers. Thus the images belonging to this group must share these constraints.

### Constructor

YAHOO.util.ImageLoader.group `( trigEl , trigAct , timeout )`

Parameters:
  `trigEl <String|HTMLElement>` The HTML element id or reference to assign the trigger event to. Can be null for no trigger
  `trigAct <String>` The type of event to assign to trigEl. Can be null for no trigger
  `timeout <Number>` Timeout (time limit) length, in seconds. Can be undefined, or <= 0, for no time limit

### Properties

#### _classImageEls - `private Array`

HTML elements having the class name that is associated with this group Elements are stored during the _foldCheck function and reused later during the fetch function. Gives a slight performance improvement when className and foldConditional are both used

#### _customTriggers - `private Array`

Collection of custom-event triggers for this group. Keeps track of each trigger's event object and event-listener-callback "fetch" function

#### _imgObjs - `private Object`

Collection of images registered with this group

#### _timeout - `private Object`

Timeout object to keep a handle on the time limit

#### _triggers - `private Array`

Collection of triggers for this group. Keeps track of each trigger's element, event, and event-listener-callback "fetch" function

#### className - `String`

Class name that will identify images belonging to the group. This class name will be removed from each element in order to fetch images. This class should have, in its CSS style definition, "background:none !important;"

#### foldConditional - `Boolean`

Flag to check if images are above the fold. If foldConditional is true, the group will check each of its image locations at page load. If any part of the image is within the client viewport, the image is displayed immediately

#### name - `String`

Name for the group. Only used to identify the group in logging statements

#### timeoutLen - `Number`

Timeout (time limit) length, in seconds

### Methods

#### _fetchByClass

`private void _fetchByClass ( )`
Finds all elements in the Dom with the class name specified in the group. Removes the class from the element in order to let the style definitions trigger the image fetching

#### _foldCheck

`private void _foldCheck ( )`
Checks the position of each image in the group. If any part of the image is within the client viewport, shows the image immediately.

#### _getFetchTimeout

`private Function _getFetchTimeout ( )`
Returns the group's fetch method, with the proper closure, for use with setTimeout

Returns: `Function`
  group's fetch method

#### _onloadTasks

`private void _onloadTasks ( )`
Setup to do in the window's onload Initiates time limit for group; executes the fold check for the images

#### addCustomTrigger

`void addCustomTrigger ( event )`
Adds a custom event trigger to the group.

Parameters:
  `event <Object>` A YAHOO.util.CustomEvent object

#### addTrigger

`void addTrigger ( trigEl , trigAct )`
Adds a trigger to the group. Call this with the same style as YAHOO.util.Event.addListener

Parameters:
  `trigEl <String|HTMLElement>` The HTML element id or reference to assign the trigger event to
  `trigAct <String>` The type of event to assign to trigEl

#### fetch

`void fetch ( )`
Displays the images in the group

#### registerBgImage

`Object registerBgImage ( domId , url )`
Registers a background image with the group

Parameters:
  `domId <String>` HTML DOM id of the image element
  `url <String>` URL for the image

Returns: `Object`
  bgImgObj that was registered, for modifying any attributes in the object

#### registerPngBgImage

`Object registerPngBgImage ( domId , url , ailProps )`
Registers an alpha-channel-type png background image with the group

Parameters:
  `domId <String>` HTML DOM id of the image element
  `url <String>` URL for the image
  `ailProps <Object>` The AlphaImageLoader properties to be set for the image Valid properties are 'sizingMethod' and 'enabled'

Returns: `Object`
  pngBgImgObj that was registered, for modifying any attributes in the object

#### registerSrcImage

`Object registerSrcImage ( domId , url , width , height )`
Registers a src image with the group

Parameters:
  `domId <String>` HTML DOM id of the image element
  `url <String>` URL for the image
  `width <Int>` pixel width of the image - defaults to image's natural size
  `height <Int>` pixel height of the image - defaults to image's natural size

Returns: `Object`
  srcImgObj that was registered, for modifying any attributes in the object

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