Answer 1

Ok so you want to know the difference between getElementById or getElementByClassName and querySelector:
querySelector uses CSS selectors to take an element from the DOM
getElementById can only select one element from the DOM. getElementByClassName and querySelector can select various elements.
getElementByClassName returns a lista with all elements that match with the given class (it happens the same if querySelector selects classes)
Hope this is helpful

Answer 2

querySelector is used for taking elements from the DOM (as you probably know)
You can use it for selecting classes
var obj = document.querySelector(“.title”)
If there are some objects with the same class:
var obj2 = document.querySelector(“.title”)[1] -> Second element with class title
You can also do the same with ids:
var obj = document.querySelector(“#title”)
And you can use querySelectorAll for selecting various elements:
var obj = document.querySelectorAll(“.title”) -> All elements with class title
You can use querySelector for taking, for example, links:
let link = document.querySelector('a[href*="https://google.com"]');

Answer 3

What do you mean? Isnt my answer working?

Answer 4

Sony Hossain Yw :)