ES6 Maps

The Map object holds key-value pairs. Any value (both objects and primitive values) may be used as either a key or a value.

See the Pen thecodelog.com - ES6 Maps 1 by Deano (@deangilewicz) on CodePen.

The Map() constructor can also receive an iterable which must produce a list of arrays, where the first item in each array is the key and the second item is the value.

See the Pen thecodelog.com - ES6 Maps 2 by Deano (@deangilewicz) on CodePen.

Since you are able to set an object as the key, using a Map can be very beneficial when storing metadata about something e.g. an element.

See the Pen thecodelog.com - ES6 Maps 3 by Deano (@deangilewicz) on CodePen.