The number of entries in this Map.

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

const { Map } = require('immutable')
const originalMap = Map()
const newerMap = originalMap.set('key', 'value')
const newestMap = newerMap.set('key', 'newer value')

originalMap
// Map {}
newerMap
// Map { "key": "value" }
newestMap
// Map { "key": "newer value" }run it

Note: set can be used in withMutations.

Returns a new Map which excludes this key.

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

const { Map } = require('immutable')
const originalMap = Map({
  key: 'value',
  otherKey: 'other value'
})
// Map { "key": "value", "otherKey": "other value" }
originalMap.delete('otherKey')
// Map { "key": "value" }run it

Note: delete can be used in withMutations.

Returns a new Map which excludes the provided keys.

const { Map } = require('immutable')
const names = Map({ a: "Aaron", b: "Barry", c: "Connor" })
names.deleteAll([ 'a', 'c' ])
// Map { "b": "Barry" }run it

Note: deleteAll can be used in withMutations.

Returns a new Map containing no keys or values.

const { Map } = require('immutable')
Map({ key: 'value' }).clear()
// Map {}run it

Note: clear 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.

const { Map } = require('immutable')
const one = Map({ a: 10, b: 20, c: 30 })
const two = Map({ b: 40, a: 50, d: 60 })
one.mergeWith((oldVal, newVal) => oldVal / newVal, two)
// { "a": 0.2, "b": 0.5, "c": 30, "d": 60 }
two.mergeWith((oldVal, newVal) => oldVal / newVal, one)
// { "b": 2, "a": 5, "d": 60, "c": 30 }run it

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().

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

const { Map } = require('immutable')
const one = Map({ a: Map({ x: 10, y: 10 }), b: Map({ x: 20, y: 50 }) })
const two = Map({ a: Map({ x: 2 }), b: Map({ y: 5 }), c: Map({ z: 3 }) })
one.mergeDeep(two)
// Map {
//   "a": Map { "x": 2, "y": 10 },
//   "b": Map { "x": 20, "y": 5 },
//   "c": Map { "z": 3 }
// }run it

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.

const { Map } = require('immutable')
const one = Map({ a: Map({ x: 10, y: 10 }), b: Map({ x: 20, y: 50 }) })
const two = Map({ a: Map({ x: 2 }), b: Map({ y: 5 }), c: Map({ z: 3 }) })
one.mergeDeepWith((oldVal, newVal) => oldVal / newVal, two)
// Map {
//   "a": Map { "x": 5, "y": 10 },
//   "b": Map { "x": 20, "y": 10 },
//   "c": Map { "z": 3 }
// }run it

Note: mergeDeepWith can be used in withMutations.

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.

const { Map } = require('immutable')
const originalMap = Map({
  subObject: Map({
    subKey: 'subvalue',
    subSubObject: Map({
      subSubKey: 'subSubValue'
    })
  })
})

const newMap = originalMap.setIn(['subObject', 'subKey'], 'ha ha!') // Map { // "subObject": Map { // "subKey": "ha ha!", // "subSubObject": Map { "subSubKey": "subSubValue" } // } // } const newerMap = originalMap.setIn( ['subObject', 'subSubObject', 'subSubKey'], 'ha ha ha!' ) // Map { // "subObject": Map { // "subKey": "subvalue", // "subSubObject": Map { "subSubKey": "ha ha ha!" } // } // }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 { Map } = require('immutable')
const originalMap = Map({
  subObject: {
    subKey: 'subvalue',
    subSubObject: {
      subSubKey: 'subSubValue'
    }
  }
})

originalMap.setIn(['subObject', 'subKey'], 'ha ha!') // Map { // "subObject": { // subKey: "ha ha!", // subSubObject: { subSubKey: "subSubValue" } // } // }run it

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.

Note: deleteIn 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)

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)

Note: mergeDeepIn can be used in withMutations.

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.

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

const { Map } = require('immutable')
const map1 = Map()
const map2 = map1.withMutations(map => {
  map.set('a', 1).set('b', 2).set('c', 3)
})
assert.equal(map1.size, 0)
assert.equal(map2.size, 3)run it

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.

Map#asImmutable

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 is safe to use in withMutations.

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

Map#asMutable

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.

Map#asMutable

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

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

Map({ a: 1, b: 2 }).map(x => 10 * x)
// Map { a: 10, b: 20 }

Collection.Keyed.mapKeys

Collection.Keyed.mapEntries

Flat-maps the Map, returning a new Map.

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

Collection.Keyed.flip

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 Keyed collection to equivalent native JavaScript Object.

Converts keys to Strings.

Shallowly converts this Keyed collection to equivalent native JavaScript Object.

Converts keys to Strings.

Shallowly converts this collection to an Array.

Shallowly converts this Collection to an Object.

Converts keys to Strings.

Returns Seq.Keyed.

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.

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.

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 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.

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 iter includes every value in this Collection.

True if this Collection includes every value in iter.