Interface List<T>

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

Returns the size of this Collection.

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.

Note: This is not a lazy operation.

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 [key, value] tuples.

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.

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

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

Returns the first value for which the predicate returns true.

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

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

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

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

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

Returns the last key for which the predicate returns true.

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

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.

Flattens nested Collections.

Will deeply flatten the Collection by default, returning a Collection of the same type, but a depth can be provided in the form of a number or boolean (where true means to shallowly flatten one level). A depth of 0 (or shallow: false) will deeply flatten.

Flattens only others Collection, not Arrays or Objects.

Note: flatten(true) operates on Collection<unknown, Collection<K, V>> and returns Collection<K, V>

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).

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

Returns the value associated with the provided index, or notSetValue if the index is beyond the bounds of the Collection.

index may be a negative number, which indexes back from the end of the Collection. s.get(-1) gets the last item in the Collection.

Returns the value associated with the provided key, or notSetValue if the Collection does not contain this key.

Note: it is possible a key may be associated with an undefined value, so if notSetValue is not provided and this method returns undefined, that does not guarantee the key was not found.

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']) // 123
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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']) // 123
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Returns a Map of Collection, 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 } ],
// }
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True if a key exists within this Collection, using Immutable.is to determine equality

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);
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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.

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

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

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

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" ]
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The shortest Collection stops interleave.

List([ 1, 2, 3 ]).interleave(
  List([ 'A', 'B' ]),
  List([ 'X', 'Y', 'Z' ])
)
// List [ 1, "A", "X", 2, "B", "Y" ]
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Since interleave() re-indexes values, it produces a complete copy, which has O(N) complexity.

Note: interleave cannot be used in withMutations.

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

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.

True if iter includes every value in this Collection.

True if this Collection includes every value in iter.

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

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

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.

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

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

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

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