Map

Immutable Map is an unordered Collection.Keyed of (key, value) pairs with O(log32 N) gets and O(log32 N) persistent sets.

type Map<K, V> extends Collection.Keyed<K, V>

Iteration order of a Map is undefined, however is stable. Multiple iterations of the same Map will iterate in the same order.

Map's keys can be of any type, and use Immutable.is to determine key equality. This allows the use of any value (including NaN) as a key.

Because Immutable.is returns equality based on value semantics, and Immutable collections are treated as values, any Immutable collection may be used as a key.

Any JavaScript object may be used as a key, however strict identity is used to evaluate key equality. Two similar looking objects will represent two different keys.

Implemented by a hash-array mapped trie.

Construction

Create a new Immutable Map.

Map<K, V>(collection?: Iterable<[K, V]>): Map<K, V>
Map<K, V>(obj: { [key: PropertyKey]: V }): Map<PropertyKey, V>

Created with the same key value pairs as the provided Collection.Keyed or JavaScript Object or expects a Collection of [K, V] tuple entries.

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

Keep in mind, when using JS objects to construct Immutable Maps, that JavaScript Object properties are always strings, even if written in a quote-less shorthand, while Immutable Maps accept keys of any type.

let obj = { 1: 'one' };
Object.keys(obj); // [ "1" ]
assert.equal(obj['1'], obj[1]); // "one" === "one"

let map = Map(obj);
assert.notEqual(map.get('1'), map.get(1)); // "one" !== undefined

Property access for JavaScript Objects first converts the key to a string, but since Immutable Map keys can be of any type the argument to get() is not altered.

Static Methods

True if the provided value is a Map.

Map.isMap(maybeMap: unknown): maybeMap is Map<unknown, unknown>

Members

The number of entries in this Map.

size: number

Persistent changes

Returns a new Map also containing the new key, value pair. If an equivalent key already exists in this Map, it will be replaced.

set(key: K, value: V): Map<K, V>

Note: set can be used in withMutations.

Returns a new Map which excludes this key.

delete(key: K): Map<K, V>

Note: delete cannot be safely used in IE8, but is provided to mirror the ES6 collection API.

Note: delete can be used in withMutations.

Returns a new Map which excludes the provided keys.

deleteAll(keys: Iterable<K>): this

Note: deleteAll can be used in withMutations.

Returns a new Map containing no keys or values.

clear(): Map<K, V>

Note: clear can be used in withMutations.

Returns a new Map having updated the value at this key with the return value of calling updater with the existing value.

update(key: K, notSetValue: V, updater: (value: V) => V): Map<K, V>
update(key: K, updater: (value: V | undefined) => V | undefined): Map<K, V>
update<R>(updater: (value: this) => R): R

Similar to: map.set(key, updater(map.get(key))).

This is most commonly used to call methods on collections within a structure of data. For example, in order to .push() onto a nested List, update and push can be used together:

When a notSetValue is provided, it is provided to the updater function when the value at the key does not exist in the Map.

However, if the updater function returns the same value it was called with, then no change will occur. This is still true if notSetValue is provided.

For code using ES2015 or later, using notSetValue is discouraged in favor of function parameter default values. This helps to avoid any potential confusion with identify functions as described above.

The previous example behaves differently when written with default values:

If no key is provided, then the updater function return value is returned as well.

This can be very useful as a way to "chain" a normal function into a sequence of methods. RxJS calls this "let" and lodash calls it "thru".

For example, to sum the values in a Map:

Note: update(key) can be used in withMutations.

Returns a new Map resulting from merging the provided Collections (or JS objects) into this Map. In other words, this takes each entry of each collection and sets it on this Map.

merge(...collections): Map<K, V>

Note: Values provided to merge are shallowly converted before being merged. No nested values are altered.

Note: merge can be used in withMutations.

Like merge(), mergeWith() returns a new Map resulting from merging the provided Collections (or JS objects) into this Map, but uses the merger function for dealing with conflicts.

mergeWith(merger: (oldVal, newVal, key) => unknown, ...collections): Map<K, V>

Note: mergeWith can be used in withMutations.

Like merge(), but when two compatible collections are encountered with the same key, it merges them as well, recursing deeply through the nested data. Two collections are considered to be compatible (and thus will be merged together) if they both fall into one of three categories: keyed (e.g., Maps, Records, and objects), indexed (e.g., Lists and arrays), or set-like (e.g., Sets). If they fall into separate categories, mergeDeep will replace the existing collection with the collection being merged in. This behavior can be customized by using mergeDeepWith().

mergeDeep(...collections): Map<K, V>

Note: Indexed and set-like collections are merged using concat()/union() and therefore do not recurse.

Note: mergeDeep can be used in withMutations.

Like mergeDeep(), but when two non-collections or incompatible collections are encountered at the same key, it uses the merger function to determine the resulting value. Collections are considered incompatible if they fall into separate categories between keyed, indexed, and set-like.

mergeDeepWith(merger: (oldVal, newVal, key) => unknown, ...collections): Map<K, V>

Note: mergeDeepWith can be used in withMutations.

Deep persistent changes

Returns a new Map having set value at this keyPath. If any keys in keyPath do not exist, a new immutable Map will be created at that key.

setIn(keyPath: Iterable<unknown>, value: unknown): Map<K, V>

Plain JavaScript Object or Arrays may be nested within an Immutable.js Collection, and setIn() can update those values as well, treating them immutably by creating new copies of those values with the changes applied.

If any key in the path exists but cannot be updated (such as a primitive like number or a custom Object like Date), an error will be thrown.

Note: setIn can be used in withMutations.

Returns a new Map having removed the value at this keyPath. If any keys in keyPath do not exist, no change will occur.

deleteIn(keyPath: Iterable<unknown>): Map<K, V>

Note: deleteIn can be used in withMutations.

Returns a new Map having applied the updater to the entry found at the keyPath.

updateIn(keyPath: Iterable<unknown>, notSetValue: unknown, updater: (value) => unknown): Map<K, V>

This is most commonly used to call methods on collections nested within a structure of data. For example, in order to .push() onto a nested List, updateIn and push can be used together:

If any keys in keyPath do not exist, new Immutable Maps will be created at those keys. If the keyPath does not already contain a value, the updater function will be called with notSetValue, if provided, otherwise undefined.

If the updater function returns the same value it was called with, then no change will occur. This is still true if notSetValue is provided.

For code using ES2015 or later, using notSetValue is discouraged in favor of function parameter default values. This helps to avoid any potential confusion with identify functions as described above.

The previous example behaves differently when written with default values:

Plain JavaScript Object or Arrays may be nested within an Immutable.js Collection, and updateIn() can update those values as well, treating them immutably by creating new copies of those values with the changes applied.

If any key in the path exists but cannot be updated (such as a primitive like number or a custom Object like Date), an error will be thrown.

Note: updateIn can be used in withMutations.

A combination of updateIn and merge, returning a new Map, but performing the merge at a point arrived at by following the keyPath. In other words, these two lines are equivalent:

map.updateIn(['a', 'b', 'c'], (abc) => abc.merge(y));
map.mergeIn(['a', 'b', 'c'], y);

mergeIn(keyPath: Iterable<unknown>, ...collections: Array<unknown>): Map<K, V>

Note: mergeIn can be used in withMutations.

A combination of updateIn and mergeDeep, returning a new Map, but performing the deep merge at a point arrived at by following the keyPath. In other words, these two lines are equivalent:

map.updateIn(['a', 'b', 'c'], (abc) => abc.mergeDeep(y));
map.mergeDeepIn(['a', 'b', 'c'], y);

mergeDeepIn(keyPath: Iterable<unknown>, ...collections: Array<unknown>): Map<K, V>

Note: mergeDeepIn can be used in withMutations.

Transient changes

Every time you call one of the above functions, a new immutable Map is created. If a pure function calls a number of these to produce a final return value, then a penalty on performance and memory has been paid by creating all of the intermediate immutable Maps.

If you need to apply a series of mutations to produce a new immutable Map, withMutations() creates a temporary mutable copy of the Map which can apply mutations in a highly performant manner. In fact, this is exactly how complex mutations like merge are done.

withMutations(mutator: (mutable: this) => unknown): Map<K, V>

As an example, this results in the creation of 2, not 4, new Maps:

Note: Not all methods can be used on a mutable collection or within withMutations! Read the documentation for each method to see if it is safe to use in withMutations.

Another way to avoid creation of intermediate Immutable maps is to create a mutable copy of this collection. Mutable copies always return this, and thus shouldn't be used for equality. Your function should never return a mutable copy of a collection, only use it internally to create a new collection.

asMutable(): this

If possible, use withMutations to work with temporary mutable copies as it provides an easier to use API and considers many common optimizations.

Note: if the collection is already mutable, asMutable returns itself.

Note: Not all methods can be used on a mutable collection or within withMutations! Read the documentation for each method to see if it allows being used in withMutations.

Returns true if this is a mutable copy (see asMutable()) and mutative alterations have been applied.

wasAltered(): boolean

The yin to asMutable's yang. Because it applies to mutable collections, this operation is mutable and may return itself (though may not return itself, i.e. if the result is an empty collection). Once performed, the original mutable copy must no longer be mutated since it may be the immutable result.

asImmutable(): this

If possible, use withMutations to work with temporary mutable copies as it provides an easier to use API and considers many common optimizations.

Sequence algorithms

Returns a new Map with values passed through a mapper function.

map<M>(mapper: (value: V, key: K, iter: this) => M, context?: unknown): Map<K, M>

Returns a new Map with keys passed through a mapper function.

mapKeys<M>(mapper: (key: K, value: V, iter: this) => M, context?: unknown): Map<M, V>

Returns a new Map with entries ([key, value] tuples) passed through a mapper function.

mapEntries<KM, VM>(mapper: (entry: [K, V], index: number, iter: this) => [KM, VM] | undefined, context?: unknown): Map<KM, VM>

Note: mapEntries() always returns a new instance, even if it produced the same entry at every step.

If the mapper function returns undefined, then the entry will be filtered.

Flat-maps the Map, returning a Map of the same type.

Similar to map(...).flatten(true).

flatMap<KM, VM>(mapper: (value: V, key: K, iter: this) => Iterable<[KM, VM]>, context?: unknown): Map<KM, VM>

Returns a new Map with only the entries for which the predicate function returns true.

filter(predicate: (value: V, key: K, iter: this) => boolean, context?: unknown): Map<K, V>

Note: filter() always returns a new instance, even if it results in not filtering out any values.

Returns a new Map with only the entries for which the predicate function returns false.

filterNot(predicate: (value: V, key: K, iter: this) => boolean, context?: unknown): this

Note: filterNot() always returns a new instance, even if it results in not filtering out any values.

Returns a new Map with the order of the entries reversed.

reverse(): this

Returns a new Map with the entries partitioned into two Maps based on the predicate function.

partition(predicate: (value: V, key: K, iter: this) => boolean, context?: unknown): [Map<K, V>, Map<K, V>]

Returns a new Map with the keys and values flipped.

flip(): Map<V, K>

Returns an OrderedMap of the same type which includes the same entries, stably sorted by using a comparator.

sort(comparator?: Comparator<V>): this & OrderedMap<K, V>

If a comparator is not provided, a default comparator uses < and >.

comparator(valueA, valueB):

• Returns 0 if the elements should not be swapped.
• Returns -1 (or any negative number) if valueA comes before valueB
• Returns 1 (or any positive number) if valueA comes after valueB
• Alternatively, can return a value of the PairSorting enum type
• Is pure, i.e. it must always return the same value for the same pair of values.

Note: sort() Always returns a new instance, even if the original was already sorted.

Note: This is always an eager operation.

Like sort, but also accepts a comparatorValueMapper which allows for sorting by more sophisticated means:

sortBy<C>(
  comparatorValueMapper: (value: V, key: K, iter: this) => C,
  comparator?: (valueA: C, valueB: C) => number
): OrderedMap<K, V>

Note: sortBy() Always returns a new instance, even if the original was already sorted.

Note: This is always an eager operation.

Returns a Map of Collection, grouped by the return value of the grouper function.

groupBy<G>(
  grouper: (value: V, key: K, iter: this) => G,
  context?: unknown
): Map<G, this>

Note: This is always an eager operation.

Conversion to JavaScript types

Deeply converts this Keyed collection to equivalent native JavaScript Object.

toJS(): Array<DeepCopy<V>> | { [key in PropertyKey]: DeepCopy<V> }

Converts keys to Strings.

Shallowly converts this Keyed collection to equivalent native JavaScript Object.

toJSON(): Array<V> | { [key in PropertyKey]: V }

Converts keys to Strings.

Shallowly converts this collection to an Array.

toArray(): Array<V> | Array<[K, V]>

Shallowly converts this Collection to an Object.

toObject(): { [key: string]: V }

Converts keys to Strings.

Conversion to Seq

Converts this Collection to a Seq of the same kind (indexed, keyed, or set).

toSeq(): Seq<K, V>

Returns a Seq.Keyed from this Collection where indices are treated as keys.

This is useful if you want to operate on a Collection.Indexed and preserve the [index, value] pairs.

The returned Seq will have identical iteration order as this Collection.

toKeyedSeq(): Seq.Keyed<K, V>

Returns an Seq.Indexed of the values of this Collection, discarding keys.

toIndexedSeq(): Seq.Indexed<V>

Returns a Seq.Set of the values of this Collection, discarding keys.

toSetSeq(): Seq.Set<V>

Value equality

True if this and the other Collection have value equality, as defined by Immutable.is().

equals(other): boolean

Note: This is equivalent to Immutable.is(this, other), but provided to allow for chained expressions.

Computes and returns the hashed identity for this Collection.

The hashCode of a Collection is used to determine potential equality, and is used when adding this to a Set or as a key in a Map, enabling lookup via a different instance.

hashCode(): number

If two values have the same hashCode, they are not guaranteed to be equal. If two values have different hashCodes, they must not be equal.

Reading values

Returns the value associated with the provided key.

get(key: K): V | undefined

True if a key exists within this Collection, using Immutable.is to determine equality.

has(key: K): boolean

True if a value exists within this Collection, using Immutable.is to determine equality.

includes(value: V): boolean

Returns the first value in this collection.

first(): V | undefined

Returns the last value in this collection.

last(): V | undefined

Reading deep values

Returns the value found by following a path of keys or indices through nested Collections.

getIn(searchKeyPath: Iterable<unknown>, notSetValue?: unknown): unknown

Plain JavaScript Object or Arrays may be nested within an Immutable.js Collection, and getIn() can access those values as well:

True if the result of following a path of keys or indices through nested Collections results in a set value.

hasIn(searchKeyPath: Iterable<unknown>): boolean

Conversion to Collections

Converts this Collection to a Map, Throws if keys are not hashable.

toMap(): Map<K, V>

Note: This is equivalent to Map(this.toKeyedSeq()), but provided for convenience and to allow for chained expressions.

Converts this Collection to a Map, maintaining the order of iteration.

toOrderedMap(): OrderedMap<K, V>

Note: This is equivalent to OrderedMap(this.toKeyedSeq()), but provided for convenience and to allow for chained expressions.

Converts this Collection to a Set, discarding keys. Throws if values are not hashable.

toSet(): Set<V>

Note: This is equivalent to Set(this), but provided to allow for chained expressions.

Converts this Collection to a Set, maintaining the order of iteration and discarding keys.

toOrderedSet(): OrderedSet<V>

Note: This is equivalent to OrderedSet(this.valueSeq()), but provided for convenience and to allow for chained expressions.

Converts this Collection to a List, discarding keys.

toList(): List<V>

This is similar to List(collection), but provided to allow for chained expressions. However, when called on Map or other keyed collections, collection.toList() discards the keys and creates a list of only the values, whereas List(collection) creates a list of entry tuples.

Converts this Collection to a Stack, discarding keys. Throws if values are not hashable.

toStack(): Stack<V>

Note: This is equivalent to Stack(this), but provided to allow for chained expressions.

Iterators

An iterator of this Collection's keys.

keys(): IterableIterator<K>

Note: this will return an ES6 iterator which does not support Immutable.js sequence algorithms. Use keySeq instead, if this is what you want.

An iterator of this Collection's values.

values(): IterableIterator<V>

Note: this will return an ES6 iterator which does not support Immutable.js sequence algorithms. Use valueSeq instead, if this is what you want.

An iterator of this Collection's entries as [ key, value ] tuples.

entries(): IterableIterator<[K, V]>

Note: this will return an ES6 iterator which does not support Immutable.js sequence algorithms. Use entrySeq instead, if this is what you want.

Collections (Seq)

Returns a new Seq.Indexed of the keys of this Collection, discarding values.

keySeq(): Seq.Indexed<K>

Returns an Seq.Indexed of the values of this Collection, discarding keys.

valueSeq(): Seq.Indexed<V>

Returns a new Seq.Indexed of [key, value] tuples.

entrySeq(): Seq.Indexed<[K, V]>

Side effects

The sideEffect is executed for every entry in the Collection.

forEach(
  sideEffect: (value: V, key: K, iter: this) => unknown,
  context?: unknown
): number

Unlike Array#forEach, if any call of sideEffect returns false, the iteration will stop. Returns the number of entries iterated (including the last iteration which returned false).

Creating subsets

Returns a new Collection of the same type representing a portion of this Collection from start up to but not including end.

slice(begin?: number, end?: number): Map<K, V>

If begin is negative, it is offset from the end of the Collection. e.g. slice(-2) returns a Collection of the last two entries. If it is not provided the new Collection will begin at the beginning of this Collection.

If end is negative, it is offset from the end of the Collection. e.g. slice(0, -1) returns a Collection of everything but the last entry. If it is not provided, the new Collection will continue through the end of this Collection.

If the requested slice is equivalent to the current Collection, then it will return itself.

Returns a new Collection of the same type containing all entries except the first.

rest(): Map<K, V>

Returns a new Collection of the same type containing all entries except the last.

butLast(): Map<K, V>

Returns a new Collection of the same type which excludes the first amount entries from this Collection.

skip(amount: number): Map<K, V>

Returns a new Collection of the same type which excludes the last amount entries from this Collection.

skipLast(amount: number): Map<K, V>

Returns a new Collection of the same type which includes entries starting from when predicate first returns false.

skipWhile(predicate: (value: V, key: K, iter: this) => boolean, context?: unknown): Map<K, V>

Returns a new Collection of the same type which includes entries starting from when predicate first returns true.

skipUntil(predicate: (value: V, key: K, iter: this) => boolean, context?: unknown): Map<K, V>

Returns a new Collection of the same type which includes the first amount entries from this Collection.

take(amount: number): Map<K, V>

Returns a new Collection of the same type which includes the last amount entries from this Collection.

takeLast(amount: number): Map<K, V>

Returns a new Collection of the same type which includes entries from this Collection as long as the predicate returns true.

takeWhile(predicate: (value: V, key: K, iter: this) => boolean, context?: unknown): Map<K, V>

Returns a new Collection of the same type which includes entries from this Collection as long as the predicate returns false.

takeUntil(predicate: (value: V, key: K, iter: this) => boolean, context?: unknown): Map<K, V>

Combination

Returns a new flattened Map, optionally only flattening to a particular depth.

flatten(depth?: number): Map<any, any>
flatten(shallow?: boolean): Map<any, any>

Reducing a value

Reduces the Collection to a value by calling the reducer for every entry in the Collection and passing along the reduced value.

reduce<R>(
  reducer: (reduction: R, value: V, key: K, iter: this) => R,
  initialReduction?: R,
  context?: unknown
): R

If initialReduction is not provided, the first item in the Collection will be used.

Reduces the Collection in reverse (from the right side).

reduceRight<R>(
  reducer: (reduction: R, value: V, key: K, iter: this) => R,
  initialReduction?: R,
  context?: unknown
): R

Note: Similar to this.reverse().reduce(), and provided for parity with Array#reduceRight.

True if predicate returns true for all entries in the Collection.

every(
  predicate: (value: V, key: K, iter: this) => boolean,
  context?: unknown
): boolean

True if predicate returns true for any entry in the Collection.

some(
  predicate: (value: V, key: K, iter: this) => boolean,
  context?: unknown
): boolean

Joins values together as a string, inserting a separator between each. The default separator is ",".

join(separator?: string = ','): string

Returns true if this Collection includes no values.

isEmpty(): boolean

For some lazy Seq, isEmpty might need to iterate to determine emptiness. At most one iteration will occur.

Returns the size of this Collection.

count(): number
count(predicate: (value: V, key: K, iter: this) => boolean, context?: unknown): number

Regardless of if this Collection can describe its size lazily (some Seqs cannot), this method will always return the correct size. E.g. it evaluates a lazy Seq if necessary.

If predicate is provided, then this returns the count of entries in the Collection for which the predicate returns true.

Returns a Seq.Keyed of counts, grouped by the return value of the grouper function.

countBy<G>(
  grouper: (value: V, key: K, iter: this) => G,
  context?: unknown
): Map<G, number>

Note: This is not a lazy operation.

Search for value

Returns the first value for which the predicate function returns true.

find(
  predicate: (value: V, key: K, iter: this) => boolean,
  context?: unknown
): V | undefined

Returns the last value for which the predicate function returns true.

findLast(
  predicate: (value: V, key: K, iter: this) => boolean,
  context?: unknown
): V | undefined

Note: predicate will be called for each entry in reverse.

Returns the first [key, value] entry for which the predicate function returns true.

findEntry(
  predicate: (value: V, key: K, iter: this) => boolean,
  context?: unknown
): [K, V] | undefined

Returns the last [key, value] entry for which the predicate function returns true.

findLastEntry(
  predicate: (value: V, key: K, iter: this) => boolean,
  context?: unknown
): [K, V] | undefined

Note: predicate will be called for each entry in reverse.

Returns the first key for which the predicate function returns true.

findKey(
  predicate: (value: V, key: K, iter: this) => boolean,
  context?: unknown
): K | undefined

Returns the last key for which the predicate function returns true.

findLastKey(
  predicate: (value: V, key: K, iter: this) => boolean,
  context?: unknown
): K | undefined

Note: predicate will be called for each entry in reverse.

Returns the key associated with the search value, or undefined.

keyOf(searchValue: V): K | undefined

Returns the last key associated with the search value, or undefined.

lastKeyOf(searchValue: V): K | undefined

Returns the maximum value in this collection. If any values are comparatively equivalent, the first one found will be returned.

max(comparator?: (valueA: V, valueB: V) => number): V | undefined

The comparator is used in the same way as Collection#sort. If it is not provided, the default comparator is >.

When two values are considered equivalent, the first encountered will be returned. Otherwise, max will operate independent of the order of input as long as the comparator is commutative. The default comparator > is commutative only when types do not differ.

If comparator returns 0 and either value is NaN, undefined, or null, that value will be returned.

Like max(), but also accepts a comparatorValueMapper which allows for comparing by more sophisticated means.

maxBy<C>(
comparatorValueMapper: (value: V, key: K, iter: this) => C,
comparator?: (valueA: C, valueB: C) => number
): V | undefined

Returns the minimum value in this collection. If any values are comparatively equivalent, the first one found will be returned.

min(comparator?: (valueA: V, valueB: V) => number): V | undefined

The comparator is used in the same way as Collection#sort. If it is not provided, the default comparator is <.

When two values are considered equivalent, the first encountered will be returned. Otherwise, min will operate independent of the order of input as long as the comparator is commutative. The default comparator < is commutative only when types do not differ.

If comparator returns 0 and either value is NaN, undefined, or null, that value will be returned.

Like min(), but also accepts a comparatorValueMapper which allows for comparing by more sophisticated means.

minBy<C>(
  comparatorValueMapper: (value: V, key: K, iter: this) => C,
  comparator?: (valueA: C, valueB: C) => number
): V | undefined

Comparison

True if iter includes every value in this Collection.

isSubset(iter: Iterable<V>): boolean

True if this Collection includes every value in iter.

isSuperset(iter: Iterable<V>): boolean