When you are writing your UI entirely in JavaScript, something is wrong.  Not only are you pushing the browser to generate a daunting amount of HTML through code, you’re also completely depending on JavaScript for anything to work on your site.  It’s Progressive Enhancement cryptonite.

To be fair, there are some reasons why you might use ExtJS for your UI:  You can get projects up and running much faster and in some groups where there isn’t a strong designer you can actually improve the consistency and look and feel of your applications.  Outside of these scenarios, I much prefer libraries like jQuery that focus on building upon the existing markup of the page rather than writing the markup for the page.

The ideal solution is one that will work for the greatest number of users. Given that, we need a solution that will use unobtrusive JavaScript to enhance a standard HTML page with customizable popup windows—rather than rely solely on JavaScript. Since straight-up HTML supports opening links in new windows by adding a target attribute to the link, we start off with a link that looks like this:

<a href="/popup.html" target="popupWindow" class="popup">Open new window</a>

Using this as a starting point, the next step is to create a simple popup window function that wraps the standard DOM method: window.open().  I use this function to do a few things:

1. Enforce default parameters rather than depend on the browser’s defaults
2. Provide defaults that favor greater accessibility, ie: scrollbars and resize
3. Allow a JavaScript object literal to be used instead of the standard configuration string

Here’s the function:

// Create a namespace for our utilities
var UTIL = UTIL || {};
UTIL.popup = UTIL.popup || {};

/**
 * Open popup window
 *
 * Opens a popup window using as little as a URL. An optional params object can
 * be passed.
 *
 * @param {String} href
 * @param {Object} params
 * @return {WindowObjectReference}
 */
UTIL.popup.open = function (href, params) {
	// Defaults (don't leave it to the browser)
	var defaultParams = {
		"width":       "800",   // Window width
		"height":      "600",   // Window height
		"top":         "0",     // Y offset (in pixels) from top of screen
		"left":        "0",     // X offset (in pixels) from left side of screen
		"directories": "no",    // Show directories/Links bar?
		"location":    "no",    // Show location/address bar?
		"resizeable":  "yes",   // Make the window resizable?
		"menubar":     "no",    // Show the menu bar?
		"toolbar":     "no",    // Show the tool (Back button etc.) bar?
		"scrollbars":  "yes",   // Show scrollbars?
		"status":      "no"     // Show the status bar?
	};

	var windowName = params["windowName"] || "new_window";

	var i, useParams = "";

	// Override defaults with custom values while we construct the params string
	for (i in defaultParams) {
		useParams += (useParams === "") ? "" : ",";
		useParams += i + "=";
		useParams += params[i] || defaultParams[i];
	}

	return window.open(href, windowName, useParams);
};

Admittedly, this part isn’t rocket science and could probably be done in a more elegant way, but it’s needed to really open things up for the next part.  Now we get to the fun stuff.  Using jQuery, we search the document for all links that have a CSS class of “popup”.  For each one we find, we add an onClick handlerthat disables the browser’s default onClick behavior for links and then opens up a popup window using the links href attribute.  Here’s the code:

$(function(){ // Run this code when the document's done loading

    // Apply this code to each link with class="popup"
    $("a.popup").each(function (i){

        // Add an onClick behavior to this link
        $(this).click(function(event) {

            // Prevent the browser's default onClick handler
            event.preventDefault();

            // Grab parameters using jQuery's data() method
            var params = $(this).data("popup") || {};

            // Use the target attribute as the window name
            if ($(this).attr("target")) {
               params.windowName = $(this).attr("target");
            }

            // Pop up the window
            var windowObject = UTIL.popup.open(this.href, params);

            // Save the window object for other code to use
            $(this).data("windowObject", windowObject);
        });
    });
});

One of the great features of jQuery that we utilize here is the data method.  This allows us to attach data to DOM elements without corrupting the HTML with non-standard attributes or tags.  Using jQuery’s ability to locate DOM elements using CSS selectors, we can bind the custom configuration object (used in our new popup function) to the links themselves.  Then, when a link is clicked, it can read it’s popup configuration and pass it to the popup window function.  In this way, we can keep our HTML standards compliant and completely separate from our JavaScript code.

Putting it all together, we can create an HTML page like this:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
	<head>
		<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
		<title>Popup Window Test</title>
		<script type="text/javascript" src="jquery-1.2.6.pack.js"></script>
		<script type="text/javascript" src="utils.js"></script>
	</head>
	<body>
		<ul>
			<li>
				This link uses defaults:
				<a href="http://google.com" target="google" class="popup">Google.com</a>
			</li>
			<li>
				This link uses custom parameters:
				<a id="custom-popup" href="http://yahoo.com" target="yahoo" class="popup">Yahoo.com</a>
			</li>
		</ul>
		<script type="text/javascript">

			// Add custom pop-up properties to the second link
			$("a#custom-popup").data("popup", {width:400,height:400, top:200, left:200});

		</script>
	</body>
</html>

If you would like to download this example, you can get it here.