DHTML in NS- The <layer> tag

This could either be a good thing, or a bad one, depending on your view. DHTML in NS 4 is quite simple, and comes down to essentially one word- Layer. I was pretty astonished myself, but its true- NS 4 relies completely on a new tag, called the <layer> tag, to spin up its DHTML magic. This new tag is dynamic in that it can be positioned anywhere on a web page (without relation to other content), moved around, its content inside updated on demand, and more.

Basic syntax

The basic syntax of the <layer> tag can't be simpler (as if any tag in HTML is complicated!):

<layer>Text inside layer</layer>

The <layer> tag is a content tag, which means you can add into it content (like <table>). Go ahead, try inserting the above code onto your page...you'll notice that the text inside the layer floats above other text, and overlaps them. Imagine a layer as a sheet of paper that resides on top of the rest of the page, and does not take up space within the flow of the document.

Layer attributes

A layer by itself can't be more boring, not to mention useless. Fortunately, there's more to it. Layers support attributes that allow you to position it using the x,y coordinates-system, give it a background, clip it (make only certain area of the layer visible), hide it from view, and so on. I've listed the most important layer attributes below:

Mix and match different attributes any way you like. Here's a sample layer that uses some of the above attributes:

<layer id="mylayer" width=100px height=70px
bgColor="yellow"><h3>A layer</h3></layer>

Notice I didn't specify the left and top attributes. When you don't, the layer is positioned where you defined it.

-Scripting layers

Here's one of the most important thing to learn about layers- how to script them. After all, its the scripts that make layers come alive. To access a layer, you need to use the following syntax:

document.layername

Accessing the layer is just the first step. Once you've accessed a layer, you can then go on and manipulate one of the layer's attributes to produce dynamic effects. I'll show a simple example where a layer's background color interchanges between red and blue:

Here's the source code I used:

    <layer id="test" width=80px height=80px></layer>

	<script language="JavaScript1.2">
	
    //variable that helps alternate between red and blue
    var thecolor=true
    //Apply a bgColor of blue as the initial layer color
    document.test1.bgColor="blue"
    function changecol(){
    //if thecolor=true
    if (thecolor)
    document.test.bgColor="blue"
    else
    document.test.bgColor="red"
    //set thecolor to the opposite of its current state
    thecolor=!thecolor
    setTimeout("changecol()",1000)
    }
    changecol()
    </script>

All of the layers' attributes are read/write, so be sure to experiment with each of them!

What is DHTML?
Beginner's Guide to DHTML
DHTML in IE 4