David Votrubec | Notes about programming

Fun with Dojo animation

Best way to learn is by doing. About a year ago when I needed to learn Dojo I created this simple animation. It is also my tribute to Avatar movie. Click the image to see it in action. It looks really cool on full screen [press F11] 🙂

Tribute to Avatar - animation build in dojo.js

How it works

When page loads dojo.addOnLoad() fires callback function. First it calculates dimension of the <img> used as background. In this case Avatar wallpaper. Then it creates overlay <div> with same dimension as background image and insert grid of tiles. Number of tiles is calculated dependending on their width and height set in config object.

var config = {
 cellHeight : 80, //px
 cellWidth : 80, //px
 timerTick: 750, //ms
 fadeOutDurr: 400, //ms
 fadeInDurr: 2200 //ms
};

Each tile has unique ID based on its position in the grid, ID is used for easy referencing of tiles for fading effects. Random tiles fade in and out revealing portions of the image underneath. To get next random cell I simply generate two random numbers (max is the number of cols/rows in the grid), compose the ID as x-y and then call dojo.byId(). Each cells also have mouseenter event listener which triggers the same fading effect. When you swift mouse over screen you will see some beautiful ‘waves’ 🙂

//create grid of tiles with StringBuilder

var str = new StringBuilder();
for(var i=0; i<rows; i++) {
	str.append('<div class="row" id="row'+ i + '">');
	for(var j=0; j<cols; j++) {
		str.append('<div class="cell" id="' + i + '-' + j +'" style="height:'+config.cellHeight+'px; width: '+(config.cellWidth-2)+'px"> </div>');
	}
	config.maxY = j;
	str.append('</div>');
}
config.maxX = i;
cellContainer.innerHTML = str.toString();

I use Javascript implementation of StringBuilder for faster string manipulation. It really pays off when building large portions of html in javascript, so I definitely recommend using it.

_fader function takes care of the fadeIn/fadeOut effect. Well, actually it is fadeOut/fadeIn but whatever…Notice the onEnd callback.

function _fader(item) {
	dojo.fadeOut({
		node: item,
		duration: config.fadeOutDurr,
		onEnd: function() {
			dojo.fadeIn({
				node: item,
				duration: config.fadeInDurr
			}).play();
		}
	}).play();
} //_fader()

Now add the event listener for mouseenter. In dojo this is done with the dojo.connect function. You can connect basically almost any object’s method to any listener or other object’s method. It’s very usefull.

dojo.forEach(dojo.query('div.cell'), function(item) {
	dojo.connect(item, 'mouseenter', function () { _fader(item)});
});

And that’s all. For the full source code see the demo.

Developer’s Medal of Honor

This is what you get if someone discoveres a bug in your code…

… more than once.

PS: It was not 10 bugs, just two, but the Medal was intended to be future-proof 🙂

jQuery.datepicker – issue with duplicate ID

I have discovered (minor) issue with jQuery Datepicker plugin:

It’s not actually datepicker’s fault, but it might be difficult to find it in a complex web page, so I decided to share it with you. Imagine that your application relies heavily on javascript, ajax, widgets etc… Widgets are created on the fly, and it happens is that two datepicker instances share the same ID. They might be generated from the same template (as was my case), or they dont have any ID at all, but were initaliazed in a certain way, more on this in future post.

Here is a sample code:

<div class="someWidget">
<input id="myId" class="datepicker"/>
</div>
....
<div class="someOtherWidget">
<input id="myId" class="datepicker"/>
</div>

and the javascript:

$('.datepicker').datepicker();

This will add datepickers on both input fields, and when they gain focus, widget will be displayed (that’s default behaviour). So far so good. But if you click on any date, it will be passed set in the first field and the first field only. Even if datepicker is displayed below the second field, the value will never be passed to it.

Why does this happen? Because of id. Datepicker uses it internally to know to which input field the date should be passed to. If you don’t supply the id in html, then datepicker will come up with its own unique id. But it will never overwrite id, if it is already set.

Hope this will help someone, it took me some time to find out what was happening.

PS:

If your datepickers share same id, and one of them is hidden, you may even get this exception: “cannot set property ‘currentDay’ of undefined”. I wanted to show it in a demo, but for some reason I was not able to reproduce it, probably there was something more involved than just ids.