Factory Map #

Extension of ECMAScript 6 Map to provide default values where no key
exists.

Replace code like:

``javascript
let map = Map();
// ...
let foo = map.get('foo');
if (foo === undefined) {
map.set('foo', 1);
}
`

with

`javascript
let map = FactoryMap();
// ...
let foo = map.get('foo', () => 1);
`

Usage ##

Use just like a normal
ECMAScript 6 Map
with the following two additions:

1. Provide an optional factory function to _get()_. If the key does
not exist in the map, then the factory function is called to create a
value. This value is inserted into the map at the given key and
returned.

`javascript
let map = new FactoryMap(); // create empty map
let value = map.get('foo', key => 'bar') // query for a key that does not exist
console.log(value); // print 'bar'
`
1. Provide an optional factory function to as the last parameter to
FactoryMap constructor. This factory function applies to all calls to
_get()_. A factory function can still be passed to _get()_ to
override.

`javascript
let map1 = new FactoryMap(key => 'bar');
let value1 = map1.get('foo')
console.log(value1); // 'bar'

let map2 = new FactoryMap([['baz', 'x']], key => 'bar');
let value2 = map2.get('foo')
console.log(value2); // 'bar'

let map3 = new FactoryMap(key => 'bar');
let value3 = map3.get('foo', key => 'bat')
console.log(value3); // 'bat'
`

License ##

Distributed under MIT license

Contributing ##

Feedback and contributions are welcome. All code changes should be
accompanied by suitable tests to be run with:

`npm test``