Map, Set Constructors

keep in mind...

1. like objects, but can hold more things including functions
2. they are directly iterable
3. non-strings can be used as keys

Research More...

1. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
2. https://javascript.info/map-set-weakmap-weakset
3. https://hackernoon.com/what-you-should-know-about-es6-maps-dc66af6b9a1e
4. http://www.deadcoderising.com/es6-working-with-sets-in-javascript/
5. https://medium.com/front-end-hacking/es6-set-vs-array-what-and-when-efc055655e1a
6. http://2ality.com/2015/01/es6-set-operations.html
7. http://www.samanthaming.com/tidbits/10-remove-array-duplicates-using-set