I would probably refactor this into a function called `createCharacter` which takes the same arguments, but returns an object that knows it's left quantity and it's dom element, like so:

```
function createCharacter(id, event_activator) {
  var character = {
    left_quantity: 0,
    element: document.getElementById(id)
  };
  character.element.addEventListener(event_activator, function() {
    character.left_quantity += 50;
    character.element.style.left = character.left_quantity;
  });
  return character;
}
```