Difference between function vs function constructors

constructors.js

function LikeButton(id) {
  this.id = id;
}
// In this case "this" will point to btn. You can read the function like this:
// function LikeButton(id) {
//   btn.id = id;
//   return btn;
// }
let btn = new LikeButton('like-button'); 

// In this case "this" will point either to undefined in strict mode 
// or window in quirks mode.
let btn = LikeButton('like-button');