MapSet
Introduction
A MapSet
is a class partially implementing the standard JavaScript Set
and Map
classes,
allowing insertion of arbitrary objects which can be indexed using a key: (item: V) => K
function supplied to the constructor, as opposed to the standard Set
which only supports object reference equality for objects.
Installation
$ npm install mapset
Description
The class behaves like a Set
for insertion: add(value: V)
and iteration of values,
and as a Map
for key-based operations like get(key: K)
, has(key: K)
and delete(key: K)
.
This enables adding unique objects in the same way as for a standard Set
, but where the uniqueness is defined by the key
function,
while at the same time allowing Map
operations to operate on the collection using keys.
To simplify typing, two interfaces defining the parts of Set
and Map
supported by MapSet
are also defined, so that
Set<V>
implements PartialSet<V>
Map<K, V>
implements PartialMap<K, V>
MapSet<K, V>
implements PartialSet<V>
and PartialMap<K, V>
This means that at an interface may refer to a PartialSet
or a PartialMap
and be implemented either by
the standard Set
and Map
classes, or by MapSet
.
Differences from Set
and Map
:
Properties missing from Set
:
keys()
- replaced by same method in Map
returning IterableIterator<K>
instead of IterableIterator<V>
entries()
- replaced by same method in Map
returning IterableIterator<[K, V]>
instead of IterableIterator<[V, V]>
delete(value: V)
- replaced by same method in Map
taking a key instead of a valuehas(value: V)
- replaced by same method in Map
taking a key instead of a valueforEach(callbackfn: (value: V, value2: V, map: Set<V>) => void, thisArg?: any)
- replaced by same method in Map
calling the callback with (value: V, key: K, map: this)
Properties missing from Map
:
[Symbol.iterator]()
- replaced by same method in Set
returning IterableIterator<V>
instead of IterableIterator<[K, V]>
set(key: K, value: V)
- replaced by add
method in Set
automatically calculating the key from the value using the key
function, to prevent inconsistent items in the MapSet
Example usage
interface Foo {
id: string;
name?: string;
age?: number;
}
const foos = new MapSet((item: Foo) => item.id); // MapSet<string, Foo>
foos.add({id: '42', name: 'John Doe'});
foos.add({id: '42', name: 'Jane Doe'}); // replaces John
foos.add({id: '79', name: 'Foo Bar'});
for (const foo of foos) {
console.log(foo);
}
foos.size; // 2
foos.has('79'); // true
foos.get('42'); // {id: '42', name: 'Jane Doe'}
foos.get('7'); // undefined
foos.delete('79'); // true
foos.has('79'); // false