Layer Object entry (and corresponding layers array entry) is created for every layer (specified by either
<ILAYER> elements, or for any element using the
position:relative style sheet positioning attributes). These objects expose various methods, properties and events.
All layers defined in a document (the Layer object and layers array are properties of the Document object) can be referenced by their name (given in their
NAME attribute) or by their index in the layers array. It's generally easier to reference layers by their name though, as their index in the layers array is determined by their z-order, from back (i.e. the furthest away) to front (the front-most layer). This isn't always the same as their
zIndex property (or
Z-INDEX attribute in the
<LAYER> element) as these don't take account of the z-order of the layer with respect to any parent/sibling layers that the particular layer you are trying to reference may have. To reference a particular layer, use :
Each layer object in the layers array has a document property, through which any child layers can be referenced through its parent layer, thus :
To reference a layer in a different window, a valid window reference will need to be used to access the document object (a property of the Window Object), to access the layer object, or layers array.
above property returns a reference to the layer object that is above the referenced layer in the z-order, of all the layers in the document. For example, if you authored two layers, one
NAMEd 'Red' and one
NAMEd 'Blue', with the 'Blue' layer having a higher z-order than the 'Red' layer, then :
would return a reference to the 'Blue' layer. (You'd need to append another property, such as
name - see below - to be able to make sense of that layer object reference). If the referenced layer is the top-most layer (or the only layer), then the
above property would return 'null'. The
above property is read-only.
This property returns a reference to the referenced layers background image (if any - it returns 'null' if the referenced layer has no background image). Each background image is an Image Object (see the Images collection), whose properties can be interrogated, or methods manipulated. The
background property can be dynamically changed.
below property is the opposite of the
above property (see above), in that it returns a reference to the layer that is immediately below (in terms of z-order) the currently referenced layer, or 'null' if the current layer is the bottom, or only layer. The
below property is read-only.
This property reflects the referenced layers background colour (as set in the
BGCOLOR attribute of either the
<LAYER> elements). It can be dynamically changed, by setting the property to a new colour, using any valid colour referencing technique (i.e. a #rrggbb hex triplet, or colour name).
clip property has 6 sub-properties, namely
clip.height, which can be used to determine, or dynamically set the clipping area (the area of the layer that is actually displayed) for the current layer.
This property reflects the referenced layers left-most point in pixels, relative to either its parent layer, or the left-most edge of the browser window if it has no parent layer. It can be manipulated to move the layer.
name property reflects the referenced layers name, as set in the
NAME attribute of either the
<LAYER> element that defines the layer.
pageX property represents the horizontal position of the referenced layer object, in pixels, relative to the main document page.
pageY property represents the vertical position of the referenced layer object, in pixels, relative to the main document page.
parentLayer property references the immediate parent layer of the currently referenced layer. If the currently referenced layer has no parent, then
parentLayer returns 'null'.
siblingAbove references the layer that is above the currently referenced layer (in terms of z-order), of all the layers that share the same parent layer. If the currently referenced layer is has no parent, or is a top-most layer, the
siblingAbove property returns 'null'.
siblingBelow references the layer that is below the currently referenced layer (in terms of z-order), of all the layers that share the same parent layer. If the currently referenced layer is has no parent, or is a bottom-most layer, the
siblingBelow property returns 'null'.
src property reflects the document that contains the content for the currently referenced layer (i.e. set by the
SRC attribute of the
<LAYER> element that defines the layer. It is read-only, that is, layer content can not be dynamically changed.
This property reflects the referenced layers top-most point in pixels, relative to either its parent layer, or the top-most edge of the browser window if it has no parent layer. It can be manipulated to move the layer.
visibility property reflects the value of the
VISIBILITY attribute (as set in the
<LAYER> element). It can be manipulated to hide the currently referenced layer or force it to inherit its parent layers (if any) visibility (by setting the
visibility property to
hide within a script function.
zIndex property can be used to determine, or dynamically set the z-order (only with respect to parent or sibling layers) of the currently referenced layers. This can be useful for dynamically changing the overlap of any layers within the document.
load method can be used to replace the contents of the referenced layer object with a new source document, referenced by the URL argument of the method, the newly loaded source document also resizing the referenced layer object according to the width argument, which is specified in pixels.
moveAbove method accepts one argument which must be a valid layer name. The layer referenced for the method is then placed above (in terms of z-order) the layer named in the argument, without physically altering its position on the screen. After the z-order change, both layers then share the same parent (if one of the layers was a child layer to start with).
moveBelow method accepts one argument which must be a valid layer name. The layer referenced for the method is then placed below (in terms of z-order) the layer named in the argument, without physically altering its position on the screen. After the z-order change, both layers then share the same parent (if one of the layers was a child layer to start with).
moveBy method moves the referenced layer horizontally (by the pixel amount given in the
x argument) and vertically (by the pixel amount given in the
y argument) relative to its current horizontal and vertical position.
moveTo layer accepts two arguments which are screen positions in pixel values. For example :
would move the layer whose
NAME is RedLayer to the position x=50, y=200 on the screen. The position can be anywhere on, or even off, the current browser viewing area.
moveToAbsolute method moves the referenced layer to the position specified by the
y arguments in the page, regardless of the position of the containing layer object.
resizeBy method resizes the referenced layer according to the pixel measurements given in the
y arguments, relative to the referenced layers current size.
resizeTo method resizes the referenced layer absolutely, according to the
y pixel measurements, regardless of its original size.
Each layer object in the Layers array/collection, fires the following events:
onblur event fires whenever the referenced layer loses the users current focus.
Whenever the user focuses (by clicking on) the referenced layer, the
onfocus event fires.
onload event is fired when the document containing the referenced layer is fully loaded, regardless of the referenced layers visibility.
When the users mouse leaves the referenced layer, the
onmouseout event is fired.
onmouseover event is fired whenever the users mouse moves over the referenced layer.
© 1995-1998, Stephen Le Hunte
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