Don't need to re-set items array

[wruth]

Hi Loiane:

I was just glancing through some of your new ES6 based code — cool stuff! I just learned about this idea of using a WeakMap for private data today, partly from your example. I will make one observation in the usage of this in your 01-Stack3.js file however. In push() and pop() you have a pattern where you re-set the array on the items WeakMap after manipulating it, for instance:

            let s = items.get(this);
            s.push(element);
            items.set(this, s);

Pretty sure it is unnecessary to set the array s after having gotten the reference to it. You didn't delete it, so you're just sharing that pointer s with the items WeakMap. That is, it's a pointer (really), not a copy of the array. So you should be able to omit the statement items.set(this, s);.

Cheers!

[loiane]

Thanks for the PR!