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Nicholas Berlette edited this page Jun 19, 2025 · 1 revision

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isExtendedSetLike

Signature

function isExtendedSetLike<T>(it: unknown): it is ExtendedSetLike<T>;

Checks whether the provided value is a ExtendedSetLike object. The ExtendedSetLike interface is the full implementation of a ExtendedSetLike object, including all the composition methods like union, intersection, difference, and symmetricDifference.

The ExtendedSetLike type is the shape of the native Set object in JavaScript after the introduction of the TC39 Proposal for Set Methods, which added the composition methods to the API.

Parameters
Name Info
it The value to check.
Returns

true if the value is a ExtendedSetLike object; otherwise, false.

Category

Guards

isExtendedSetLikeConstructor

Signature

function isExtendedSetLikeConstructor(
  it: unknown,
): it is ExtendedSetLikeConstructor;

Checks if a given value appears to be a ExtendedSetLikeConstructor function, including a prototype property that appears to be a ExtendedSetLike object.

Parameters
Name Info
it The value to check.
Returns

true if the value is a ExtendedSetLikeConstructor function; otherwise, false.

Category

Guards

isReadonlyCollection

Signature

function isReadonlyCollection<T>(it: unknown): it is ReadonlyCollection<T>;

Checks whether the provided value is a ReadonlyCollection object. The ReadonlyCollection interface is the minimum requirement for a value to be used in the composition methods found in ExtendedSetLike implementations, such as union, intersection, difference, and symmetricDifference.

This type is the bare minimal requirement for a value to be considered a "set-like" object in JavaScript, and only requires the has, keys, and size members to be present. As such, native Set objects and also native Map objects both qualify as ReadonlyCollection objects. For a more specific check, see isSetLike or isExtendedSetLike, which check for the full API of a Set object, with or without the composition methods added by the TC39 proposal, respectively.

Parameters
Name Info
it The value to check.
Returns

true if the value is a ReadonlyCollection object; otherwise, false.

Category

Guards

isReadonlyCollectionConstructor

Signature

function isReadonlyCollectionConstructor(
  it: unknown,
): it is ReadonlyCollectionConstructor;

Checks if a given value appears to be a ReadonlyCollectionConstructor function, including a prototype property that appears to be a ReadonlyCollection object.

Parameters
Name Info
it The value to check.
Returns

true if the value appears to be a ReadonlyCollectionConstructor function; otherwise, false.

Category

Guards

isSetLike

Signature

function isSetLike<T>(it: unknown): it is SetLike<T>;

Checks whether the provided value is a SetLike object. The SetLike interface is the base implementation of a ExtendedSetLike object, without any additional composition methods like union or intersection.

This type is the shape of the native Set object in JavaScript prior to the introduction of the TC39 Proposal for Set Methods, which added the composition methods to the API.

Parameters
Name Info
it The value to check.
Returns

true if the value is a SetLike object; otherwise, false.

Category

Guards

isSetLikeConstructor

Signature

function isSetLikeConstructor(it: unknown): it is SetLikeConstructor;

Checks if a given value appears to be a SetLikeConstructor function, including a prototype property that appears to be a SetLike object.

Parameters
Name Info
it The value to check.
Returns

true if the value is a SetLikeConstructor function; otherwise, false.

Category

Guards

SupportedSetLike

Signature

export type SupportedSetLike<T = unknown> =
  Exclude<keyof ExtendedSetLike<T>, keyof SetLike<T>> extends
    keyof globalThis.Set<T> ? ExtendedSetLike<T> : SetLike<T>;

This type represents either the full ExtendedSetLike interface, or the SetLike interface, depending on whether the current environment supports composition methods introduced by the TC39 Set Methods Proposal.

If the current environment supports the composition methods, this type will resolve to the ExtendedSetLike interface. Otherwise, it will resolve to the SetLike interface.

Type Parameters
  • T (default: unknown)
See Also

SupportedSetLikeConstructor

Signature

export type SupportedSetLikeConstructor =
  Exclude<keyof ExtendedSetLikeConstructor, keyof SetLikeConstructor> extends
    keyof globalThis.SetConstructor ? ExtendedSetLikeConstructor
    : SetLikeConstructor;

This type represents either the full ExtendedSetLikeConstructor interface, or the SetLikeConstructor interface, depending on whether the current environment supports composition methods introduced by the TC39 Set Methods Proposal.

If the current environment supports the composition methods, this type will resolve to the ExtendedSetLikeConstructor interface. Otherwise, it will resolve to the SetLikeConstructor interface.

See Also

ExtendedSetLike

A ExtendedSetLike object is a collection of values, where each value may only occur once. The values in a ExtendedSetLike can be either primitive values or object references. The keys of a ExtendedSetLike are the same as the values.

Type Parameters
  • T (default: unknown)
Extends SetLike<T>

Methods

union

union<U>(
    other: ReadonlyCollection<U>,
  ): ExtendedSetLike<T | U>;
Parameters
Name Info
other The other set-like object to merge with this one.
Returns

a new ExtendedSetLike object containing all the elements in this ExtendedSetLike object and also all the elements in the other.

intersection

intersection<U>(
    other: ReadonlyCollection<U>,
  ): ExtendedSetLike<T & U>;
Parameters
Name Info
other The other set-like object to intersect with this one.
Returns

a new ExtendedSetLike object containing all the elements which are both in this ExtendedSetLike object and in the other.

difference

difference<U>(
    other: ReadonlyCollection<U>,
  ): ExtendedSetLike<T>;
Parameters
Name Info
other The other set-like object to compare with this one.
Returns

a new ExtendedSetLike object containing all the elements in this ExtendedSetLike object which are not also in the other.

symmetricDifference

symmetricDifference<U>(
    other: ReadonlyCollection<U>,
  ): ExtendedSetLike<T | U>;
Parameters
Name Info
other The other set-like object to compare with this one.
Returns

a new ExtendedSetLike object containing all the elements which are in either this ExtendedSetLike object or in the other, but not in both.

isSubsetOf

isSubsetOf<U>(
    other: ReadonlyCollection<U>,
  ): boolean;
Parameters
Name Info
other The other set-like object to compare with this one.
Returns

a boolean indicating whether all the elements in this ExtendedSetLike object are also in the other.

isSupersetOf

isSupersetOf<U>(
    other: ReadonlyCollection<U>,
  ): boolean;
Parameters
Name Info
other The other set-like object to compare with this one.
Returns

a boolean indicating whether all the elements in the other are also in this ExtendedSetLike object.

isDisjointFrom

isDisjointFrom<U>(
    other: ReadonlyCollection<U>,
  ): boolean;
Parameters
Name Info
other The other set-like object to compare with this one.
Returns

a boolean indicating whether this ExtendedSetLike object has no elements in common with the other.

ExtendedSetLikeConstructor

Represents a constructor function for an ExtendedSetLike object.

Properties

prototype

readonly prototype: ExtendedSetLike<any>;

ReadonlyCollection

Set-like objects are collections of unique values (each value may only occur once). The ReadonlyCollection interface defines the bare minimum requirements for an object to be considered "set-like" in JavaScript; that is, it must have:

  • a has method, which tests whether a given value is present in the set, returning a boolean value indicating the result.
  • a keys method, which returns an IterableIterator for the keys present in the set. Since set collections are keyed by their values, the keys method actually iterates over the values in the set.
  • a read-only size property (getter), which returns the number of values in the set at any given time.

This interface the base for the SetLike interface (hence its name), which extends it with additional methods like add, delete, clear, forEach, values, and entries to provide a more complete API for working with Set- like collections in JavaScript. Prior to the TC39 Proposal for Set Methods, the SetLike interface was the shape of the native Set API in JavaScript.

Following the introduction of the TC39 Proposal for Set Methods, the methods for set composition (union, intersection, difference, etc.) were added to the Set API, which necessitated the creation of the ExtendedSetLike interface to represent the full API for set-like collections in JavaScript.

Those methods require their arguments to implement the ReadonlyCollection interface, rather than the full SetLike or ExtendedSetLike. This means you can call Set.prototype.union with a Set, Map, or even an IterableWeakSet object, since they all implement the ReadonlyCollection API.

See Also
Type Parameters
  • T (default: unknown)

Properties

size

readonly size: number;
Returns

The number of elements in the collection.

Methods

has

has(value: T): boolean;

Tests whether a given value is present in the collection.

Parameters
Name Info
value The value to lookup.
Returns

true if the value is in the collection; otherwise, false.

keys

keys(): IterableIterator<T>;

Gets an IterableIterator for the keys present in the collection.

Returns

An iterator of the keys in the collection.

ReadonlyCollectionConstructor

Represents a constructor function for a ReadonlyCollection object, which is the base implementation of a ExtendedSetLike object, without any of the additional composition methods like union or intersection.

See Also
  • ExtendedSetLike for the full interface with composition methods.
  • SetLike for the core interface without composition methods.

Properties

prototype

readonly prototype: ReadonlyCollection<unknown>;

SetLike

Represents the core functionality of a SetLike object, which is the base implementation of a ExtendedSetLike object, without any additional composition methods (union, intersection, difference, etc). This was the native Set API prior to the TC39 Set Methods Proposal's introduction.

See Also
Type Parameters
  • T (default: unknown)
Extends Iterable<T>, ReadonlyCollection<T>

Properties

size

readonly size: number;
Returns

The number of elements in the collection.

[Symbol.toStringTag]

readonly [Symbol.toStringTag]: string;

Methods

add

add(value: T): this;

Adds the given value to the collection, if it does not already exist.

Parameters
Name Info
value The value to add.
Returns

The collection.

has

has(value: T): boolean;

Tests whether a key is present in the collection.

Parameters
Name Info
value The key to lookup.
Returns

true if the value is in the collection; otherwise, false.

clear

clear(): void;

Removes all values from the collection.

delete

delete(value: T): boolean;

Removes a value from the collection.

Parameters
Name Info
value The vakue to remove.
Returns

true if the operation was successful; otherwise, false.

forEach

forEach<This = void>(
    cb: (this: This, value: T, value2: T, set: this) => void,
    thisArg?: This,
  ): void;

Executes a provided function once per each entry in the collection. The callback is invoked with the current value for both the first and second arguments (to maintain a similar signature as forEach on other iterable objects like Map and Array).

Parameters
Name Info
cb The callback to execute.
thisArg The value to use as this when executing the callback.
Returns

Nothing.

keys

keys(): IterableIterator<T>;
Returns

an Iterable of the values in the collection.

values

values(): IterableIterator<T>;
Returns

an IterableIterator for the values present in the collection.

entries

entries(): IterableIterator<
    [T, T]
  >;
Returns

an IterableIterator of the entries present in the collection. Each entry is a tuple containing the key and value for each element.

[Symbol.iterator]

[Symbol.iterator](): IterableIterator<
    T
  >;

Returns an iterator of the values in the set.

SetLikeConstructor

Represents a constructor function for a SetLike object, which is the base implementation of a ExtendedSetLike object, without any of the additional composition methods like union or intersection.

See Also
  • ExtendedSetLike for the full interface with composition methods.
  • SetLike for the core interface without composition methods.

Properties

prototype

readonly prototype: SetLike<any>;
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