How does data binding work in AngularJS?

Question

How does data binding work in the AngularJS framework?

I haven\'t found technical details on their site. It\'s more or less clear how it works when data

Answer 1

Misko already gave an excellent description of how the data bindings work, but I would like to add my view on the performance issue with the data binding.

As Misko stated, around 2000 bindings are where you start to see problems, but you shouldn't have more than 2000 pieces of information on a page anyway. This may be true, but not every data-binding is visible to the user. Once you start building any sort of widget or data grid with two-way binding you can easily hit 2000 bindings, without having a bad UX.

Consider, for example, a combo box where you can type text to filter the available options. This sort of control could have ~150 items and still be highly usable. If it has some extra feature (for example a specific class on the currently selected option) you start to get 3-5 bindings per option. Put three of these widgets on a page (e.g. one to select a country, the other to select a city in the said country, and the third to select a hotel) and you are somewhere between 1000 and 2000 bindings already.

Or consider a data-grid in a corporate web application. 50 rows per page is not unreasonable, each of which could have 10-20 columns. If you build this with ng-repeats, and/or have information in some cells which uses some bindings, you could be approaching 2000 bindings with this grid alone.

I find this to be a huge problem when working with AngularJS, and the only solution I've been able to find so far is to construct widgets without using two-way binding, instead of using ngOnce, deregistering watchers and similar tricks, or construct directives which build the DOM with jQuery and DOM manipulation. I feel this defeats the purpose of using Angular in the first place.

I would love to hear suggestions on other ways to handle this, but then maybe I should write my own question. I wanted to put this in a comment, but it turned out to be way too long for that...

TL;DR
The data binding can cause performance issues on complex pages.