Answers for "how to get class in javascript"

javascript get element by class

var elementsArray = document.getElementsByClassName("someclassname");

js get class property

let element = document.querySelector('.preset');
let style = getComputedStyle(element);
let bg = style.backgroundColor;

get class of object javascript

class Dog{}
var dog = new Dog();
if(dog instanceof Dog){
  console.log("Is dog");
}