Dark mode feature, changing img src in init() does not work

In the controller I have

  init(){
    this._super(...arguments);
    document.body.classList.add("darkMode");
    document.getElementById('mode').src = 'assets/images/logo-white'
  }

and in the handlebars:

<img id="mode" src="assets/images/logo-black.png" alt="white-theme" width="188px" height="56px">

While trying to apply a dark-theme to my project, I successfully added the class to it, but when I tried changing the logo img src by finding its id, it crashes (as in nothing is showing anymore), this is probably because the init() does everything before loading the actual image and cannot take the id from img. I have no solution to this yet, so any idea would be awesome.

I am doing it this way just to test, later I will add an if clause to test whether the user wants to have dark-mode on or not