List

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

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

const { List, Set } = require('immutable')

const emptyList = List()
// List []

const plainArray = [ 1, 2, 3, 4 ]
const listFromPlainArray = List(plainArray)
// List [ 1, 2, 3, 4 ]

const plainSet = Set([ 1, 2, 3, 4 ])
const listFromPlainSet = List(plainSet)
// List [ 1, 2, 3, 4 ]

const arrayIterator = plainArray[Symbol.iterator]()
const listFromCollectionArray = List(arrayIterator)
// List [ 1, 2, 3, 4 ]

listFromPlainArray.equals(listFromCollectionArray) // true
listFromPlainSet.equals(listFromCollectionArray) // true
listFromPlainSet.equals(listFromPlainArray) // truerun it

The number of items in this List.

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

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.

const originalList = List([ 0 ]);
// List [ 0 ]
originalList.set(1, 1);
// List [ 0, 1 ]
originalList.set(0, 'overwritten');
// List [ "overwritten" ]
originalList.set(2, 2);
// List [ 0, undefined, 2 ]

List().set(50000, 'value').size;
// 50001run it

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).

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

List([ 0, 1, 2, 3, 4 ]).delete(0);
// List [ 1, 2, 3, 4 ]run it

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.

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

List([ 0, 1, 2, 3, 4 ]).insert(6, 5)
// List [ 0, 1, 2, 3, 4, 5 ]run it

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.

List([ 1, 2, 3, 4 ]).clear()
// List []run it

Note: clear can be used in withMutations.

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

List([ 1, 2, 3, 4 ]).push(5)
// List [ 1, 2, 3, 4, 5 ]run it

Note: push can be used in withMutations.

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

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.

List([ 1, 2, 3, 4 ]).pop()
// List[ 1, 2, 3 ]

Note: pop can be used in withMutations.

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

List([ 2, 3, 4]).unshift(1);
// List [ 1, 2, 3, 4 ]run it

Note: unshift can be used in withMutations.

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

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.

List([ 0, 1, 2, 3, 4 ]).shift();
// List [ 1, 2, 3, 4 ]run it

Note: shift 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.

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.

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.

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

const { List } = require('immutable')
const list = List([ 0, 1, 2, List([ 3, 4 ])])
list.setIn([3, 0], 999);
// List [ 0, 1, 2, List [ 999, 4 ] ]run it

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.

const { List } = require('immutable')
const list = List([ 0, 1, 2, { plain: 'object' }])
list.setIn([3, 'plain'], 'value');
// List([ 0, 1, 2, { plain: 'value' }])run it

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.

const { List } = require('immutable')
const list = List([ 0, 1, 2, List([ 3, 4 ])])
list.deleteIn([3, 0]);
// List [ 0, 1, 2, List [ 4 ] ]run it

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.

const { List } = require('immutable')
const list = List([ 0, 1, 2, { plain: 'object' }])
list.removeIn([3, 'plain']);
// List([ 0, 1, 2, {}])run it

Note: deleteIn cannot be safely used in withMutations.

Note: mergeIn can be used in withMutations.

Map#mergeIn

Note: mergeDeepIn can be used in withMutations.

Map#mergeDeepIn

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.

Map#withMutations

An alternative API for withMutations()

Map#asMutable

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.

Map#wasAltered

Map#asImmutable

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

Note: concat can be used in withMutations.

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

List([ 1, 2 ]).map(x => 10 * x)
// List [ 10, 20 ]run it

Flat-maps the List, returning a new List.

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

Returns a new Collection of the same type with only the entries for which the predicate function returns false.

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.

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

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
• 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.

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 it

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:

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 Collection.Keyed of Collection.Keyeds, grouped by the return value of the grouper function.

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 it

Deeply converts this Indexed collection to equivalent native JavaScript Array.

Shallowly converts this Indexed collection to equivalent native JavaScript Array.

Shallowly converts this collection to an Array.

Shallowly converts this Collection to an Object.

Converts keys to Strings.

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

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

In case the Collection is not empty returns the first element of the Collection. In case the Collection is empty returns the optional default value if provided, if no default value is provided returns undefined.

In case the Collection is not empty returns the last element of the Collection. In case the Collection is empty returns the optional default value if provided, if no default value is provided returns undefined.

Returns Seq.Indexed.

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

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

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 it

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

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

Returns a Collection of the same type with separator between each item in this Collection.

Returns a Collection of the same type with the provided collections interleaved into this collection.

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

const { List } = require('immutable')
List([ 1, 2, 3 ]).interleave(List([ 'A', 'B', 'C' ]))
// List [ 1, "A", 2, "B", 3, "C" ]run it

The shortest Collection stops interleave.

List([ 1, 2, 3 ]).interleave(
  List([ 'A', 'B' ]),
  List([ 'X', 'Y', 'Z' ])
)
// List [ 1, "A", "X", 2, "B", "Y" ]run it

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

Note: interleave cannot be used in withMutations.

Splice returns a new indexed Collection by replacing a region of this Collection 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 Collection. s.splice(-2) splices after the second to last item.

const { List } = require('immutable')
List([ 'a', 'b', 'c', 'd' ]).splice(1, 2, 'q', 'r', 's')
// List [ "a", "q", "r", "s", "d" ]run it

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

Note: splice cannot be used in withMutations.

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

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

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

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

Returns the first value for which the predicate returns true.

Returns the last value for which the predicate returns true.

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

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

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

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

Returns the key for which the predicate returns true.

Returns the last key for which the predicate returns true.

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

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

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

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

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:

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.

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:

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

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.

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 it

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.

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

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.

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

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.

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.

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.

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.

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 it

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

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

An iterator of this Collection's 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.

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.

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

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

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

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

The sideEffect is executed for every entry in the Collection.

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.

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.

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

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

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

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

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.

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.

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

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

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.

const { List } = require('immutable')
List([ 'dog', 'frog', 'cat', 'hat', 'god' ])
  .takeUntil(x => x.match(/at/))
// List [ "dog", "frog" ]run it

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

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

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

Returns true if this Collection includes no values.

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

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

Note: This is not a lazy operation.

True if iter includes every value in this Collection.

True if this Collection includes every value in iter.