Seq describes a lazy operation, allowing them to efficiently chain
use of all the higher-order collection methods (such as map and filter)
by not creating intermediate collections.
type Seq<K, V> extends Collection<K, V>Seq is immutable — Once a Seq is created, it cannot be
changed, appended to, rearranged or otherwise modified. Instead, any
mutative method called on a Seq will return a new Seq.
Seq is lazy — Seq does as little work as necessary to respond to any
method call. Values are often created during iteration, including implicit
iteration when reducing or converting to a concrete data structure such as
a List or JavaScript Array.
For example, the following performs no work, because the resulting
Seq's values are never iterated:
const { Seq } = require('immutable')
const oddSquares = Seq([ 1, 2, 3, 4, 5, 6, 7, 8 ])
.filter(x => x % 2 !== 0)
.map(x => x * x)Once the Seq is used, it performs only the work necessary. In this
example, no intermediate arrays are ever created, filter is called three
times, and map is only called once:
oddSquares.get(1); // 9Any collection can be converted to a lazy Seq with Seq().
const { Map } = require('immutable')
const map = Map({ a: 1, b: 2, c: 3 })
const lazySeq = Seq(map)run itSeq allows for the efficient chaining of operations, allowing for the
expression of logic that can otherwise be very tedious:
lazySeq
.flip()
.map(key => key.toUpperCase())
.flip()
// Seq { A: 1, B: 1, C: 1 }As well as expressing logic that would otherwise seem memory or time
limited, for example Range is a special kind of Lazy sequence.
const { Range } = require('immutable')
Range(1, Infinity)
.skip(1000)
.map(n => -n)
.filter(n => n % 2 === 0)
.take(2)
.reduce((r, n) => r * n, 1)
// 1006008run itSeq is often used to provide a rich collection API to JavaScript Object.
Seq({ x: 0, y: 1, z: 2 }).map(v => v * 2).toObject();
// { x: 0, y: 2, z: 4 }Seq<S>(seq: S): S
Seq<K, V>(collection: Collection.Keyed<K, V>): Seq.Keyed<K, V>
Seq<T>(collection: Collection.Set<T>): Seq.Set<T>
Seq<T>(collection: Collection.Indexed<T> | Iterable<T> | ArrayLike<T>): Seq.Indexed<T>
Seq<V>(obj: {[key: string]: V}): Seq.Keyed<string, V>
Seq<K, V>(): Seq<K, V>
Seq.isSeq(maybeSeq: unknown): boolean
Some Seqs can describe their size lazily. When this is the case, size will be an integer. Otherwise it will be undefined.
size: number | undefinedBecause Sequences are lazy and designed to be chained together, they do
not cache their results. For example, this map function is called a total
of 6 times, as each join iterates the Seq of three values.
cacheResult(): this
var squares = Seq([ 1, 2, 3 ]).map(x => x x)
squares.join() + squares.join()
If you know a Seq will be used multiple times, it may be more
efficient to first cache it in memory. Here, the map function is called
only 3 times.
var squares = Seq([ 1, 2, 3 ]).map(x => x x).cacheResult()
squares.join() + squares.join()Use this method judiciously, as it must fully evaluate a Seq which can be a burden on memory and possibly performance.
Note: after calling cacheResult, a Seq will always have a size.
Returns a new Seq with values passed through a
mapper function.
map<M>(mapper: (value: V, key: K, iter: this) => M,
context?: unknown): Seq<K, M>
map<M>(mapper: (value: V, key: K, iter: this) => M,
context?: unknown): Seq<M, M>
Collection#map()const { Seq } = require('immutable')
Seq([ 1, 2 ]).map(x => 10 * x)
// Seq [ 10, 20 ]Note: map() always returns a new instance, even if it produced the same
value at every step.
Note: used only for sets.
Flat-maps the Seq, returning a Seq of the same type.
flatMap<M>(mapper: (value: V, key: K, iter: this) => Iterable<M>,
context?: unknown): Seq<K, M>
flatMap<M>(mapper: (value: V, key: K, iter: this) => Iterable<M>,
context?: unknown): Seq<M, M>
Collection#flatMap()Similar to seq.map(...).flatten(true).
Note: Used only for sets.
filter<F>(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown): Seq<K, F>
filter(predicate: (value: V, key: K, iter: this) => unknown,
context?: unknown): this
Collection#filter()partition<F, C>(predicate: (this: C, value: V, key: K, iter: this) => boolean,
context?: C): [Seq<K, V>, Seq<K, F>]
partition<C>(predicate: (this: C, value: V, key: K, iter: this) => unknown,
context?: C): [this, this]
Collection#partition()Returns a new Collection of the same type with only the entries for which
the predicate function returns false.
filterNot(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown): this
Collection#filterNot()const { Map } = require('immutable')
Map({ a: 1, b: 2, c: 3, d: 4}).filterNot(x => x % 2 === 0)
// Map { "a": 1, "c": 3 }run it
Note: filterNot() always returns a new instance, even if it results in
not filtering out any values.
Returns a new Collection of the same type in reverse order.
reverse(): this
Collection#reverse()Returns a new Collection of the same type which includes the same entries,
stably sorted by using a comparator.
sort(comparator?: Comparator<V>): this
Collection#sort()If a comparator is not provided, a default comparator uses < and >.
comparator(valueA, valueB):
0 if the elements should not be swapped.-1 (or any negative number) if valueA comes before valueB1 (or any positive number) if valueA comes after valueBPairSorting enum typeWhen sorting collections which have no defined order, their ordered
equivalents will be returned. e.g. map.sort() returns OrderedMap.
const { Map } = require('immutable')
Map({ "c": 3, "a": 1, "b": 2 }).sort((a, b) => {
if (a < b) { return -1; }
if (a > b) { return 1; }
if (a === b) { return 0; }
});
// OrderedMap { "a": 1, "b": 2, "c": 3 }run itNote: 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?: Comparator<C>): this
Collection#sortBy()const { Map } = require('immutable')
const beattles = Map({
John: { name: "Lennon" },
Paul: { name: "McCartney" },
George: { name: "Harrison" },
Ringo: { name: "Starr" },
});
beattles.sortBy(member => member.name);run it
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>
Collection#groupBy()Note: This is always an eager operation.
const { List, Map } = require('immutable')
const listOfMaps = List([
Map({ v: 0 }),
Map({ v: 1 }),
Map({ v: 1 }),
Map({ v: 0 }),
Map({ v: 2 })
])
const groupsOfMaps = listOfMaps.groupBy(x => x.get('v'))
// Map {
// 0: List [ Map{ "v": 0 }, Map { "v": 0 } ],
// 1: List [ Map{ "v": 1 }, Map { "v": 1 } ],
// 2: List [ Map{ "v": 2 } ],
// }run itTrue if this and the other Collection have value equality, as defined
by Immutable.is().
equals(other: unknown): boolean
Collection#equals()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.
hashCode(): number
Collection#hashCode()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.
const a = List([ 1, 2, 3 ]);
const b = List([ 1, 2, 3 ]);
assert.notStrictEqual(a, b); // different instances
const set = Set([ a ]);
assert.equal(set.has(b), true);run itIf two values have the same hashCode, they are not guaranteed
to be equal. If two values have different hashCodes,
they must not be equal.
get<NSV>(key: K, notSetValue: NSV): V | NSV
get(key: K): V | undefined
Collection#get()True if a key exists within this Collection, using Immutable.is
to determine equality
has(key: K): boolean
Collection#has()True if a value exists within this Collection, using Immutable.is
to determine equality
includes(value: V): boolean
Collection#includes()contains()first<NSV>(notSetValue: NSV): V | NSV
first(): V | undefined
Collection#first()last<NSV>(notSetValue: NSV): V | NSV
last(): V | undefined
Collection#last()Returns the value found by following a path of keys or indices through nested Collections.
getIn(searchKeyPath: Iterable<unknown>, notSetValue?: unknown): unknown
Collection#getIn()const { Map, List } = require('immutable')
const deepData = Map({ x: List([ Map({ y: 123 }) ]) });
deepData.getIn(['x', 0, 'y']) // 123run it
Plain JavaScript Object or Arrays may be nested within an Immutable.js Collection, and getIn() can access those values as well:
const { Map, List } = require('immutable')
const deepData = Map({ x: [ { y: 123 } ] });
deepData.getIn(['x', 0, 'y']) // 123run it
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
Collection#hasIn()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".
update<R>(updater: (value: this) => R): R
Collection#update()For example, to sum a Seq after mapping and filtering:
const { Seq } = require('immutable')
function sum(collection) {
return collection.reduce((sum, x) => sum + x, 0)
}
Seq([ 1, 2, 3 ])
.map(x => x + 1)
.filter(x => x % 2 === 0)
.update(sum)
// 6run it
Deeply converts this Collection to equivalent native JavaScript Array or Object.
toJS(): Array<DeepCopy<V>> | {[key: string]: DeepCopy<V>}
Collection#toJS()Collection.Indexed, and Collection.Set become Array, while
Collection.Keyed become Object, converting keys to Strings.
Shallowly converts this Collection to equivalent native JavaScript Array or Object.
toJSON(): Array<V> | {[key: string]: V}
Collection#toJSON()Collection.Indexed, and Collection.Set become Array, while
Collection.Keyed become Object, converting keys to Strings.
Shallowly converts this collection to an Array.
toArray(): Array<V> | Array<[K, V]>
Collection#toArray()Collection.Indexed, and Collection.Set produce an Array of values.
Collection.Keyed produce an Array of [key, value] tuples.
Shallowly converts this Collection to an Object.
toObject(): {[key: string]: V}
Collection#toObject()Converts keys to Strings.
Converts this Collection to a Map, Throws if keys are not hashable.
toMap(): Map<K, V>
Collection#toMap()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>
Collection#toOrderedMap()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>
Collection#toSet()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>
Collection#toOrderedSet()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>
Collection#toList()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.
const { Map, List } = require('immutable')
var myMap = Map({ a: 'Apple', b: 'Banana' })
List(myMap) // List [ [ "a", "Apple" ], [ "b", "Banana" ] ]
myMap.toList() // List [ "Apple", "Banana" ]run itConverts this Collection to a Stack, discarding keys. Throws if values are not hashable.
toStack(): Stack<V>
Collection#toStack()Note: This is equivalent to Stack(this), but provided to allow for
chained expressions.
Converts this Collection to a Seq of the same kind (indexed, keyed, or set).
toSeq(): Seq<K, V>
Collection#toSeq()Returns a Seq.Keyed from this Collection where indices are treated as keys.
toKeyedSeq(): Seq.Keyed<K, V>
Collection#toKeyedSeq()This is useful if you want to operate on an Collection.Indexed and preserve the [index, value] pairs.
The returned Seq will have identical iteration order as this Collection.
const { Seq } = require('immutable')
const indexedSeq = Seq([ 'A', 'B', 'C' ])
// Seq [ "A", "B", "C" ]
indexedSeq.filter(v => v === 'B')
// Seq [ "B" ]
const keyedSeq = indexedSeq.toKeyedSeq()
// Seq { 0: "A", 1: "B", 2: "C" }
keyedSeq.filter(v => v === 'B')
// Seq { 1: "B" }run itReturns an Seq.Indexed of the values of this Collection, discarding keys.
toIndexedSeq(): Seq.Indexed<V>
Collection#toIndexedSeq()Returns a Seq.Set of the values of this Collection, discarding keys.
toSetSeq(): Seq.Set<V>
Collection#toSetSeq()An iterator of this Collection's keys.
keys(): IterableIterator<K>
Collection#keys()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>
Collection#values()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]>
Collection#entries()Note: this will return an ES6 iterator which does not support
Immutable.js sequence algorithms. Use entrySeq instead, if this is
what you want.
[Symbol.iterator](): IterableIterator<unknown>
Collection#[Symbol.iterator]()Returns a new Seq.Indexed of the keys of this Collection, discarding values.
keySeq(): Seq.Indexed<K>
Collection#keySeq()Returns an Seq.Indexed of the values of this Collection, discarding keys.
valueSeq(): Seq.Indexed<V>
Collection#valueSeq()Returns a new Seq.Indexed of [key, value] tuples.
entrySeq(): Seq.Indexed<[K, V]>
Collection#entrySeq()The sideEffect is executed for every entry in the Collection.
forEach(sideEffect: (value: V, key: K, iter: this) => unknown,
context?: unknown): number
Collection#forEach()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).
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
Collection#slice()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(): this
Collection#rest()Returns a new Collection of the same type containing all entries except the last.
butLast(): this
Collection#butLast()Returns a new Collection of the same type which excludes the first amount
entries from this Collection.
skip(amount: number): this
Collection#skip()Returns a new Collection of the same type which excludes the last amount
entries from this Collection.
skipLast(amount: number): this
Collection#skipLast()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): this
Collection#skipWhile()const { List } = require('immutable')
List([ 'dog', 'frog', 'cat', 'hat', 'god' ])
.skipWhile(x => x.match(/g/))
// List [ "cat", "hat", "god" ]run it
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
Collection#skipUntil()const { List } = require('immutable')
List([ 'dog', 'frog', 'cat', 'hat', 'god' ])
.skipUntil(x => x.match(/hat/))
// List [ "hat", "god" ]run it
Returns a new Collection of the same type which includes the first amount
entries from this Collection.
take(amount: number): this
Collection#take()Returns a new Collection of the same type which includes the last amount
entries from this Collection.
takeLast(amount: number): this
Collection#takeLast()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): this
Collection#takeWhile()const { List } = require('immutable')
List([ 'dog', 'frog', 'cat', 'hat', 'god' ])
.takeWhile(x => x.match(/o/))
// List [ "dog", "frog" ]run it
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): this
Collection#takeUntil()const { List } = require('immutable')
List([ 'dog', 'frog', 'cat', 'hat', 'god' ])
.takeUntil(x => x.match(/at/))
// List [ "dog", "frog" ]run it
Returns a new Collection of the same type with other values and collection-like concatenated to this one.
concat(...valuesOrCollections: Array<unknown>): Collection<unknown, unknown>
Collection#concat()For Seqs, all entries will be present in the resulting Seq, even if they have the same key.
flatten(depth?: number): Collection<unknown, unknown>
flatten(shallow?: boolean): Collection<unknown, unknown>
Collection#flatten()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
Collection#reduce()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
Collection#reduceRight()True if predicate returns true for all entries in the Collection.
every(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown): boolean
Collection#every()True if predicate returns true for any entry in the Collection.
some(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown): boolean
Collection#some()Joins values together as a string, inserting a separator between each.
The default separator is ",".
join(separator?: string): string
Collection#join()Returns true if this Collection includes no values.
isEmpty(): boolean
Collection#isEmpty()count(): number
count(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown): number
Collection#count()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>
Collection#countBy()Note: This is not a lazy operation.
Returns the first value for which the predicate returns true.
find(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown,
notSetValue?: V): V | undefined
Collection#find()Returns the last value for which the predicate returns true.
findLast(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown,
notSetValue?: V): V | undefined
Collection#findLast()Note: predicate will be called for each entry in reverse.
Returns the first [key, value] entry for which the predicate returns true.
findEntry(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown,
notSetValue?: V): [K, V] | undefined
Collection#findEntry()Returns the last [key, value] entry for which the predicate
returns true.
findLastEntry(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown,
notSetValue?: V): [K, V] | undefined
Collection#findLastEntry()Note: predicate will be called for each entry in reverse.
Returns the key for which the predicate returns true.
findKey(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown): K | undefined
Collection#findKey()Returns the last key for which the predicate returns true.
findLastKey(predicate: (value: V, key: K, iter: this) => boolean,
context?: unknown): K | undefined
Collection#findLastKey()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
Collection#keyOf()Returns the last key associated with the search value, or undefined.
lastKeyOf(searchValue: V): K | undefined
Collection#lastKeyOf()Returns the maximum value in this collection. If any values are comparatively equivalent, the first one found will be returned.
max(comparator?: Comparator<V>): V | undefined
Collection#max()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?: Comparator<C>): V | undefined
Collection#maxBy()const { List, } = require('immutable');
const l = List([
{ name: 'Bob', avgHit: 1 },
{ name: 'Max', avgHit: 3 },
{ name: 'Lili', avgHit: 2 } ,
]);
l.maxBy(i => i.avgHit); // will output { name: 'Max', avgHit: 3 }run it
Returns the minimum value in this collection. If any values are comparatively equivalent, the first one found will be returned.
min(comparator?: Comparator<V>): V | undefined
Collection#min()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?: Comparator<C>): V | undefined
Collection#minBy()const { List, } = require('immutable');
const l = List([
{ name: 'Bob', avgHit: 1 },
{ name: 'Max', avgHit: 3 },
{ name: 'Lili', avgHit: 2 } ,
]);
l.minBy(i => i.avgHit); // will output { name: 'Bob', avgHit: 1 }run it
True if iter includes every value in this Collection.
isSubset(iter: Iterable<V>): boolean
Collection#isSubset()True if this Collection includes every value in iter.
isSuperset(iter: Iterable<V>): boolean
Collection#isSuperset()