How to create jQuery like object functions with JavaScript

I'm working on trying to create a small library of helper functions for a project.

At the moment, I've setup a lot of functions in global scope that look like this:

function addClass(el, className) {
   el.classList.add(className);
}

var target = document.querySelector('.target);
addClass(target, "added-class");

With adding a class as an example, I'd like to follow a jQuery like function so that it gets called like this:

var target = document.querySelector('.target);
target.addClass("added-class");

How can I setup a function so that it is called this way?