One of the most important things in AngularJS is the data binding. In fact I think it is so important it should be one of the first things you should get to know if you start to write Angular apps. It should be explained more and it shouldn’t be just “the magic that we won’t cover right now”.
The real magic behind Angular’s data binding is called dirty checking. Basically every time you write
in the background a new watch for the expression
is being created that on every $digest cycle will be evaluated and if the value of the model is changed, the DOM will be updated. Thanks to this dirty checking we are also able to use plain old JS object as our model. How data binding works is explained in detail in this great article – http://angular-tips.com/blog/2013/08/watch-how-the-apply-runs-a-digest/. I also recommend to read Misko’s answer to this StackOverflow question on why dirty checking is not a bad thing, unless of course it is used in a bad way. This is why we should understand how data binding works.