many-keys-map

many-keys-map

A Map subclass with support for multiple keys for one entry.

A ManyKeysMap object is identical to a regular Map, with the exception that it only supports a sequence of keys as key, instead of a single key. This will let you attach a value to a specific combination of keys, instead of a single key.

const regularMap = new Map();
regularMap.set('hello', true);

const manyKeysMap = new ManyKeysMap();
manyKeysMap.set(['hello', 'world'], true);

This is useful when the keys cannot be easily combined (i.e. object)

const handlers = new ManyKeysMap();
handlers.set([element, 'click'], onClickFn);
handlers.set([element, 'keypress', {passive: true}], onKeypressFn);
// Since objects are stored by reference, it’s best to stringify `options` object like the above
handlers.set([element, 'keypress', JSON.stringify({passive: true})], onKeypressFn);

The number of keys allowed is unlimited and their order matters.

Install

$ npm install many-keys-map

Usage

It should work exactly the same as a Map, except that the key must always be an array.

import ManyKeysMap from 'many-keys-map';

const groups = new ManyKeysMap();
groups.set([header, 'admin'], true);
groups.set([target, 'tools'], [1, 'any value is supported']);

const data = new ManyKeysMap([
	[['hello key'], 'value'],
	[[42, null], new Date()]
]);

data.get(['hello key']);
// => 'value'

data.get([42, null]);
// => date Object

data.get(['42']);
// => undefined

data.has([Symbol()]);
// => false

for (const [keys, value] of data) {
	console.log(keys);
	console.log(value);
}
// => ['hello key']
// => 'value'
// => [42, null]
// => date Object

Allowed keys

1. Keys must always be an array, e.g. .set([a, b], 'hello')
2. Only the values in the keys array are stored, not the array itself — so future changes to the array won’t be reflected in the map.
3. ManyKeysMap supports any number of keys, any of these are valid and different: .get([a]) and .get([a, b, c, d, e, f, g])
4. The order of keys matters, so .get([a, b]) is different from .get([b, a])
5. The keys can be anything supported by Map.

Related

• many-keys-weakmap - A WeakMap subclass with support for multiple keys for one entry.