Why is the class not added to the element when using addClass?

Question

Angular

Good afternoon! Please tell me how to solve the problem.
I use this code:

var flID = '#preview' + $num;
var elemFL = angular.element(document.querySelector(flID));
elemFL.addClass('arrow_top');
console.log(elemFL);

Judging by the console, the class "arrow_top" was added to the element
[div#preview1.arrow_top]
but it is not in the page code.
<div id="preview0" class="">
Why is this happening?

Answer 1

Ну и еще вы разные элементы смотрите