A bi-directional map, with unique keys to unique values. Internally, its a map and its inverse map which allows value to be looked up through key, and key through value.
Eg. email id <-> person name.

const BiMap = require('extra-bimap');
// : all Map() functions available

var m = new BiMap();
// BiMap [Map] {}

m.set(1, 'a');
// BiMap [Map] { 1 => 'a' }

m.set(2, 'b');
// BiMap [Map] { 1 => 'a', 2 => 'b' }

m.set(2, 'a');
// Error: BiMap pair is not unique

m.inverse;
// BiMap [Map] { 'a' => 1, 'b' => 2 }

m.inverse.set('a', 2);
// Error: BiMap pair is not unique

m.inverse.set('b', 3);
// BiMap [Map] { 'a' => 1, 'b' => 3 }

m.inverse.inverse
// BiMap [Map] { 1 => 'a', 3 => 'b' }

m.delete(1);
// BiMap [Map] { 3 => 'b' }

m.inverse.has('a')
// false

reference

Name	Action
BiMap	Creates a bi-directional map, with unique keys to unique values.
inverse	Gives reversed bi-directional map.
clear	Removes all elements from map.
delete	Removes the specified element from map.
set	Adds or updates an element with a specified key and a value to map.
size	Same as Map.
entries	Same as Map.
forEach	Same as Map.
get	Same as Map.
has	Same as Map.
keys	Same as Map.
values	Same as Map.
@@iterator	Same as Map.