How does Angular.JS work at the lowest level?

Question

Angular

I read articles, googled, but it's still not entirely clear how real-time change tracking is implemented.
Here, for example , Make your own AngularJS , the author himself calls scope.$digest();
At the moment my guess is:
it's an infinite loop comparing 2 objects.
But then iterations on different machines work at different speeds.
And if there are a lot of ng directives, is it very expensive?

Answer 1

In fact, everything is correct in the article, this is not an infinite loop, but the old and current values ​​\u200b\u200bare compared in it, in case of a difference, "callbacks" are called.
$digest() is called on every corner and on every sneeze: after $timout, after $http, after ng-click, etc., therefore, the illusion of "real-time change tracking" is created.

And if there are a lot of ng directives, is it very expensive?

On modern hardware and browser, more than 10M comparisons per second can occur, so applications with a small $digest with a small number of 1000-20k watches are fast (depending on the watches).
Also now in all frameworks there is a trend towards (isolated) components, therefore, with the correct construction of a web application (1000 components x 1000 watches) -> and 1M watches will work quickly (1ms).