smap.js

var map = new Map();
map.set('foo', 'bar');
map.set(0, 42);

// Filter map by a function
map.filter(function(key, value) {
   return typeof key == 'string';
});
=> new Map([[0, 42]])

// Merge Maps
map.merge(new Map([['baz', 'thing']]));
=> new Map([[0, 42], ['baz', 'thing']])

// map.get with a default
map.fetch('NON_EXISTANT', 'default');
=> 'default'

// Invert map (makes keys->values and vice versa)
map.invert();
=> new Map([[42, 0], ['thing', 'baz']])

// Destructive filter (inline map delete)
map.reject(function(key, value) {
  return typeof key == 'string';
});
map.has('thing');
=> false

// Remove all items
map.clear();

// Check if Map has no items
map.isEmpty();
=> true

npm install smap