Matthew Roper

As part of the interface for a web application, I wrote the following code to implement a modal dialogue box in JavaScript (similar to the Lightbox effect).

While there are a few different examples of this effect that I could have used, I was after something straight-forward and lightweight with clear separation of design (CSS) and presentation logic (JavaScript).

function DialogOverlay(content, container) {
 
	// Manage arguments and assign defaults,
	if (typeof container == 'undefined' ) container = document.body;
	if (null == (this.container = $(container))) throw("container is not valid");
 
	// Assign instance variables
	this.content = content;
	this.overlay = new Element('div', { 'class': 'overlay' }).hide();
	this.dialog = new Element('div', { 'class': 'dialog' }).hide();
 
	// Hide the overlay when clicked. Ignore clicks on the dialog.
	Event.observe(this.overlay, 'click', this.hide.bindAsEventListener(this));
	Event.observe(this.dialog, 'click',  function(event) { Event.stop(event) });
 
	// Insert the elements into the DOM
	this.dialog.insert(this.content);
	this.container.insert(this.overlay);
	this.container.insert(this.dialog);
 
	// Content may have been hidden if it is embedded in the page
	content.show();
	this.dialog.hide();
}
 
DialogOverlay.prototype.show = function() {
	new Effect.Appear(this.overlay, { duration: 0.5,  to: 0.8 });
	this.dialog.show();
	return this;
};
DialogOverlay.prototype.hide = function(event) {
	this.dialog.hide();
	this.overlay.hide();
	return this;
};

Adding a dialogue object to your page is simple:

<script type="text/javascript">
	var dialog = new Element('div');
	dialog.insert(new Element('h2').insert('Dialogue'));
	var overlay = new DialogOverlay(dialog);
</script>

In addition, you'll need some CSS to control the presentation of the overlay and dialogue box:

.overlay {
	width: 100%;
	height: 100%;
	background: black;
	position: fixed;
	top: 0;
	left: 0;
	z-index: 98;
}
.dialog {
	width: 50%;
	min-height: 50%;
	background: white;
	position: fixed;
	top: 25%;
	left: 25%;
	z-index: 99;
}

I uploaded the JavaScript class (overlay.js) and made a quick example page to show it working.