githubmirror/immutable-js

website/docs/OrdererMap.mdx
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Julien Deniau
Doc as mdx instead of export from .d.ts file (#2104)
24 май 2025, 00:47
24 май 2025, 00:4721de701
import Repl from '@/repl/Repl.tsx';
import CodeLink from '@/mdx-components/CodeLink.tsx';

# OrderedMap

A type of [`Map`](../Map/) that maintains the order of iteration according to when entries were set.

<Signature code={`type OrderedMap<K, V> extends Map<K, V>`} />

The iteration behavior of OrderedMap is the same as native ES6 Map and JavaScript Object.

Note that `OrderedMap` are more expensive than non-ordered Map and may consume more memory. OrderedMap#set is amortized `O(log32 N)`, but not stable.

Let's look at the following example to see the difference between `Map` and `OrderedMap`:

<Repl defaultValue={`Map({a: 1, c: 3, b: 2})`} />

The `b` key is re-located on the second position.

<Repl defaultValue={`OrderedMap({a: 1, c: 3, b: 2})`} />

The `b` key is still on the third position.

## Similar API with `Map`

`OrderedMap` has the exact same API as [`Map`](../Map/). The only new method is <CodeLink to="isOrderedMap">OrderedMap.isOrderedMap(maybeOrderedMap)</CodeLink> to check if a value is an `OrderedMap`.

## Construction

<MemberLabel label="OrderedMap()" />

Creates a new Immutable OrderedMap.

<Signature
  code={`OrderedMap<K, V>(collection?: Iterable<[K, V]>): OrderedMap<K, V>
OrderedMap<V>(obj: { [key: PropertyKey]: V }): OrderedMap<PropertyKey, V>`}
/>

Note: `OrderedMap` is a factory function and not a class, and does not use the `new` keyword during construction.

<Repl defaultValue={`OrderedMap({ a: 1, b: 2 })`} />

## Static Methods

<MemberLabel label="OrderedMap.isOrderedMap()" />

True if the provided value is an OrderedMap.

<Signature code={`OrderedMap.isOrderedMap(maybeOrderedMap): boolean`} />