List

Lists are ordered indexed dense collections, much like a JavaScript Array.

type List<T> extends Collection.Indexed<T>

Lists are immutable and fully persistent with O(log32 N) gets and sets, and O(1) push and pop.

Lists implement Deque, with efficient addition and removal from both the end (push, pop) and beginning (unshift, shift).

Unlike a JavaScript Array, there is no distinction between an "unset" index and an index set to undefined. List#forEach visits all indices from 0 to size, regardless of whether they were explicitly defined.

Construction

Create a new immutable List containing the values of the provided collection-like.

List<T>(collection?: Iterable<T> | ArrayLike<T>): List<T>

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

Static methods

List.isList(value: any): boolean

List.of<T>(...values: Array<T>): List<T>

Members

The number of items in this List.

size: number

Persistent changes

Returns a new List which includes value at index. If index already exists in this List, it will be replaced.

set(index: number, value: T): List<T>

index may be a negative number, which indexes back from the end of the List. v.set(-1, "value") sets the last item in the List.

If index larger than size, the returned List's size will be large enough to include the index.

Note: set can be used in withMutations.

Returns a new List which excludes this index and with a size 1 less than this List. Values at indices above index are shifted down by 1 to fill the position.

This is synonymous with list.splice(index, 1).

delete(index: number): List<T>

index may be a negative number, which indexes back from the end of the List. v.delete(-1) deletes the last item in the List.

Note: delete cannot be safely used in IE8.

Since delete() re-indexes values, it produces a complete copy, which has O(N) complexity.

Note: delete cannot be used in withMutations.

Returns a new List with value at index with a size 1 more than this List. Values at indices above index are shifted over by 1.

insert(index: number, value: T): List<T>

This is synonymous with list.splice(index, 0, value).

Since insert() re-indexes values, it produces a complete copy, which has O(N) complexity.

Note: insert cannot be used in withMutations.

Returns a new List with 0 size and no values in constant time.

clear(): List<T>

Note: clear can be used in withMutations.

Returns a new List with the provided values appended, starting at this List's size.

push(...values: Array<T>): List<T>

Note: push can be used in withMutations.

Returns a new List with a size one less than this List, excluding the last index in this List.

pop(): List<T>

Note: this differs from Array#pop because it returns a new List rather than the removed value. Use last() to get the last value in this List.

Note: pop can be used in withMutations.

Returns a new List with the provided values prepended, shifting other values ahead to higher indices.

unshift(...values: Array<T>): List<T>

Note: unshift can be used in withMutations.

Returns a new List with a size one less than this List, excluding the first index in this List, shifting all other values to a lower index.

shift(): List<T>

Note: this differs from Array#shift because it returns a new List rather than the removed value. Use first() to get the first value in this List.

Note: shift can be used in withMutations.

Returns a new List with an updated value at index with the return value of calling updater with the existing value, or notSetValue if index was not set. If called with a single argument, updater is called with the List itself.

update(index: number, notSetValue: T, updater: (value: T) => T): List<T>
update(index: number, updater: (value: T | undefined) => T | undefined): List<T>
update<R>(updater: (value: this) => R): R

index may be a negative number, which indexes back from the end of the List. v.update(-1) updates the last item in the List.

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 a List after mapping and filtering:

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

Returns a new List with size size. If size is less than this List's size, the new List will exclude values at the higher indices. If size is greater than this List's size, the new List will have undefined values for the newly available indices.

setSize(size: number): List<T>

When building a new List and the final size is known up front, setSize used in conjunction with withMutations may result in the more performant construction.

Deep persistent changes

Returns a new List 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): List<T>

Index numbers are used as keys to determine the path to follow in the List.

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.

Note: setIn can be used in withMutations.

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

deleteIn(keyPath: Iterable<unknown>): List<T>

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

Note: deleteIn cannot be safely used in withMutations.

updateIn(keyPath: Iterable<unknown>, notSetValue: unknown, updater: (value: unknown) => unknown): this
updateIn(keyPath: Iterable<unknown>, updater: (value: unknown) => unknown): this

Note: updateIn can be used in withMutations.

mergeIn(keyPath: Iterable<unknown>, ...collections: Array<unknown>): this

Note: mergeIn can be used in withMutations.

mergeDeepIn(keyPath: Iterable<unknown>, ...collections: Array<unknown>): this

Note: mergeDeepIn can be used in withMutations.

Transient changes

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

withMutations(mutator: (mutable: this) => unknown): List<T>

An alternative API for withMutations()

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

asMutable(): List<T>

See

wasAltered(): boolean

See

asImmutable(): this

See

Sequence algorithms

Returns a new List with other values or collections concatenated to this one.

concat<C>(...valuesOrCollections: Array<Iterable<C> | C>): List<T | C>

Note: concat can be used in withMutations.

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

map<M>(mapper: (value: T, key: number, iter: this) => M, context?: unknown): List<M>

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

mapKeys<M>(mapper: (value: T, key: number, iter: this) => M, context?: unknown): List<M>

See

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

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

Flat-maps the List, returning a new List.

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

flatMap<M>(mapper: (value: T, key: number, iter: this) => Iterable<M>, context?: unknown): List<M>

Returns a new List with only the values for which the predicate function returns true.

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

filter<F extends T>(predicate: (value: T, index: number, iter: this) => value is F, context?: unknown): List<F>

Returns a new List with the values for which the predicate function returns false and another for which is returns true.

partition<F extends T, C>(predicate: (this: C, value: T, index: number, iter: this) => value is F, context?: C): [List<T>, List<F>]

Returns a List "zipped" with the provided collection.

Like zipWith, but using the default zipper: creating an Array.

zip<U>(other: Collection<unknown, U>): List<[T, U]>
zip<U, V>(other: Collection<unknown, U>, other2: Collection<unknown, V>): List<[T, U, V]>

Returns a List "zipped" with the provided collections.

Unlike zip, zipAll continues zipping until the longest collection is exhausted. Missing values from shorter collections are filled with undefined.

zipAll<U>(other: Collection<unknown, U>): List<[T, U]>
zipAll<U, V>(other: Collection<unknown, U>, other2: Collection<unknown, V>): List<[T, U, V]>

Note: Since zipAll will return a collection as large as the largest input, some results may contain undefined values. TypeScript cannot account for these without cases (as of v2.5).

Returns a List "zipped" with the provided collections by using a custom zipper function.

zipWith<U, Z>(zipper: (value: T, otherValue: U) => Z, otherCollection: Collection<unknown, U>): List<Z>
zipWith<U, V, Z>(zipper: (value: T, otherValue: U, thirdValue: V) => Z, otherCollection: Collection<unknown, U>, thirdCollection: Collection<unknown, V>): List<Z>
zipWith<Z>(zipper: (...values: Array<unknown>) => Z, ...collections: Array<Collection<unknown, unknown>>): List<Z>

Returns a new List with its values shuffled thanks to the Fisher–Yates algorithm. It uses Math.random, but you can provide your own random number generator.

shuffle(random?: () => number): this

Returns a new List with only the values for which the predicate function returns false.

filterNot(predicate: (value: T, index: number, 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 List with the order of the values reversed.

reverse(): List<T>

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

sort(comparator?: (valueA, valueB) => number): List<T>

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.

When sorting collections which have no defined order, their ordered equivalents will be returned. e.g. map.sort() returns OrderedMap.

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(comparatorValueMapper: (value: T, iter: this) => C, comparator?: (a, b) => number): List<T>

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 List grouped by the return value of the grouper function.

groupBy<G>(grouper: (value: T, index: number, iter: this) => G, context?: unknown): Map<G, List<T>>

Note: This is not a lazy operation.

Conversion to JavaScript types

Deeply converts this List to a JavaScript Array.

toJS(): Array<DeepCopy<T>>

Shallowly converts this Indexed collection to equivalent native JavaScript Array.

toJSON(): Array<T>

Shallowly converts this collection to an Array.

toArray(): Array<T>

Shallowly converts this List to a JavaScript Object.

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

Convert keys to strings.

Reading values

Returns the value at index.

get(index: number): T

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

has(key): boolean

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

includes(value: T): boolean

Returns the first value in this collection.

first(): T

Returns the last value in this collection.

last(): T

Conversion to Seq

Converts this List to a Seq of the same kind (indexed).

toSeq(): Seq.Indexed<T>

If this is a collection of [key, value] entry tuples, it will return a Seq.Keyed of those entries.

fromEntrySeq(): List<T>

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

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

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

toKeyedSeq(): Seq.Keyed<number, T>

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

toIndexedSeq(): Seq.Indexed<T>

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

toSetSeq(): Seq.Set<T>

Combination

Returns a new List with the separator inserted between each value in this List.

interpose(separator: T): List<T>

Returns a new List with the values from each collection interleaved.

interleave(...collections: Array<Collection<unknown, T>>): List<T>

The resulting Collection includes the first item from each, then the second from each, etc.

The shortest Collection stops interleave.

Since interleave() re-indexes values, it produces a complete copy, which has O(N) complexity.

Note: interleave() cannot be used in withMutations.

Returns a new List by replacing a region of this List with new values. If values are not provided, it only skips the region to be removed.

index may be a negative number, which indexes back from the end of the List. s.splice(-2) splices after the second to last item.

splice(index: number, removeNum: number, ...values: Array<T>): List<T>

Since splice() re-indexes values, it produces a complete copy, which has O(N) complexity.

Note: splice cannot be used in withMutations.

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

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

Search for value

Returns the first index at which a given value can be found in the Collection, or -1 if it is not present.

indexOf(value: T): number

Returns the last index at which a given value can be found in the Collection, or -1 if it is not present.

lastIndexOf(value: T): number

Returns the first index in the Collection where a value satisfies the provided predicate function. Otherwise -1 is returned.

findIndex(predicate: (value: T, index: number, iter: this) => boolean, context?: unknown): number

Returns the last index in the Collection where a value satisfies the provided predicate function. Otherwise -1 is returned.

findLastIndex(predicate: (value: T, index: number, iter: this) => boolean, context?: unknown): number

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

find(predicate: (value: T, index: number, iter: this) => boolean, context?: unknown): T | undefined

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

findLast(predicate: (value: T, index: number, iter: this) => boolean, context?: unknown): T | 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: T, key: number, iter: this) => boolean, context?: unknown): [number, T] | undefined

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

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

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

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

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

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

keyOf(searchValue: T): number | undefined

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

lastKeyOf(searchValue: T): number | undefined

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

max(comparator?: (valueA: T, valueB: T) => number): T | 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: T, key: number, iter: this) => C,
comparator?: (valueA: C, valueB: C) => number
): T | undefined

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

min(comparator?: (valueA: T, valueB: T) => number): T | 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: T, key: number, iter: this) => C,
comparator?: (valueA: C, valueB: C) => number
): T | undefined

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 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.

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.

toList(): List<V>

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): this

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(): List<T>

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

butLast(): List<T>

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

skip(amount: number): List<T>

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

skipLast(amount: number): List<T>

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): List<T>

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): this

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

take(amount: number): List<T>

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

takeLast(amount: number): List<T>

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): List<T>

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): List<T>

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
reduce<R>(reducer: (reduction: V | R, value: V, key: K, iter: this) => R): 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
reduceRight<R>(reducer: (reduction: V | R, value: V, key: K, iter: this) => R): 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.

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