Why I don't like KnockoutJS

There should not be complex javascript code in the data-binding side.

In the other hand when you talk about separation between UI and HTML (or templates), I feel that when I am not using knockoutjs I have to use a lot of jquery selectors in the functionaly, so I don't have a simple javascript binding in the html, but i have a complex html selection in the "functionality" side. This means that my -templates- are very independent from my functionality but the functionality itself is very tied to the templates.

What do you think about this?

(I am a js beginner)

I see your point, however when you do this:

var viewModel = {
    clickedMe: funtion(){
   //my whatever logic here.
   //tighted with dom manipulation.
   if(foo)$("#some-id").attr("enable", "true");
   };
 }

$("#some-id").click(function(e){e.preventDef....(); viewModel.clickedMe();}); //wire up in javascript.

What you have right there is html as a placeholder which makes no sense without the javascript that tights the knots, and javascript is doing two very different things, having your model logic mixed with dom manipulation. Your rendering logic is separated in two parts instead of one.

HTML is not what it used to be. Using knockout.js you can have your domain model in javascript, and your rendering logic in html/templates. Now the rendering logic is in only one part.

Knockout appears very powerful and I would guess it appeals greatly to the Silverlight and WPF crowd since they are more familiar with the whole MVVM approach.

I have some of the same concerns as you've mentioned (about mixing concerns). I'm not a Knockout user, but I've heard there are ways to wire it up without putting code in the attributes, but it seems most examples I see are combining the two.

Brandon Satrum has actually extended it somewhat here... http://userinexperience.com/?p=689

I've been using KO for some time now and really like it. I prefer clean javascript over clean markup in web applications where you'd typically use KO. Recently our design team dropped a complete html rewrite of an app and all we had to do was to copy the databinding attributes over, without even touching the underlying javascript layer - saved us a lot of time!

Unobtrusive KnockOut.js might solve your problem: http://joel.net/unobtrusive-data-binding-for-knockout-js

FYI - some of your dislikes regarding mixed concerns has been addressed in 1.3 and a beta was released earlier today. Check it out at link text

What if the bindings worked like this:

$knockoutJs.databind("body > ul > li > a", "click: registerClick, enable: !hasClickedTooManyTimes()");

Soo, combine a CSS selector with the data-bind attribute?

I've been playing around with KO and while I tend to agree with you on the mix of HTML+JS, the power of the observable seems pretty good

Gareth

You couldn't possibly have got it more wrong.

What you want is the logic of the views to reside within the views, and the business logic to be part of your code.

It's a more higher level separation than HTML/CSS and JS. MVVM is a clean separation between UI/Models.

$("#searchText") <- referring to UI from within business logic.

-_-

You couldn't possibly have got it more wrong.

What you want is the logic of the views to reside within the views, and the business logic to be part of your code.

It's a more higher level separation than HTML/CSS and JS. MVVM is a clean separation between UI/Models.

$("#searchText") <- referring to UI from within business logic. = (eventual) FAIL -_-