is

Type guards and predicates for common JavaScript values.

Checks use standard JavaScript and web-platform types available in current browsers, Node, Deno, and Bun. A true type-guard result narrows the input to the type shown in its signature.

import is from "@rcompat/is";

is.array#

Checks whether a value is an array.

is.array(x: unknown): x is unknown[];

is.arraybuffer#

Checks whether a value is an ArrayBuffer.

is.arraybuffer(x: unknown): x is ArrayBuffer;

is.bigint#

Checks whether a value is a bigint.

is.bigint(x: unknown): x is bigint;

is.blank#

Checks whether a value is an empty or whitespace-only string.

is.blank(x: unknown): x is string;

is.blob#

Checks whether a value is a Blob.

is.blob(x: unknown): x is Blob;

is.boolish#

Checks whether a value is the string "true" or "false".

is.boolish(x: unknown): x is Boolish;

is.boolean#

Checks whether a value is a boolean.

is.boolean(x: unknown): x is boolean;

is.branded#

Checks whether an object owns a symbol brand.

is.branded<S extends symbol>(
    x: unknown,
    brand: S,
  ): x is Record<S, () => unknown>;

is.bytes#

Checks whether a value is a Uint8Array.

is.bytes(x: unknown): x is Uint8Array;

is.date#

Checks whether a value is a Date.

is.date(x: unknown): x is Date;

is.defined#

Checks whether a value is not undefined.

is.defined<T>(x: T): x is Exclude<T, undefined>;

is.dict#

Checks whether a value is a plain object.

is.dict(x: unknown): x is Dict;

is.empty#

Checks whether a string, collection, or object is empty.

is.empty(x: unknown): boolean;

is.error#

Checks whether a value is an Error.

is.error(x: unknown): x is Error;

is.f32#

Checks whether a number is exactly representable as a float32.

is.f32(x: unknown): x is number;

is.f32array#

Checks whether a value is a Float32Array.

is.f32array(x: unknown): x is Float32Array;

is.f64array#

Checks whether a value is a Float64Array.

is.f64array(x: unknown): x is Float64Array;

is.falsy#

Checks whether a value is falsy.

is.falsy(x: unknown): boolean;

is.file#

Checks whether a value is a File.

is.file(x: unknown): x is File;

is.finite#

Checks whether a value is a finite number or bigint.

is.finite(x: unknown): x is bigint | number;

is.function#

Checks whether a value is callable.

is.function(x: unknown): x is UnknownFunction;

is.int#

Checks whether a value is an integer number or bigint.

is.int(x: unknown): x is bigint | number;

is.iterable#

Checks whether a value implements the iterable protocol.

is.iterable(x: unknown): x is Iterable<unknown>;

is.json#

Checks whether a value has a direct JSON representation.

Sparse arrays are rejected because JSON serialization replaces holes with null.

is.json(x: unknown): x is JSONValue;

is.map#

Checks whether a value is a Map.

is.map(x: unknown): x is Map<unknown, unknown>;

is.nan#

Checks whether a value is NaN.

is.nan(x: unknown): x is number;

is.nonempty#

Checks whether a nullable value is nonempty.

is.nonempty<T>(x: T | Nullish): x is T;

is.newable#

Checks whether a value is constructible with new.

is.newable(x: unknown): x is Newable;

is.null#

Checks whether a value is null.

is.null(x: unknown): x is null;

is.nullish#

Checks whether a value is null or undefined.

is.nullish(x: unknown): x is Nullish;

is.number#

Checks whether a value is a number, including NaN.

is.number(x: unknown): x is number;

is.numeric#

Checks whether a value is a decimal numeric string.

is.numeric(x: unknown): x is string;

is.object#

Checks whether a value is a non-null object.

is.object(x: unknown): x is object;

is.primitive#

Checks whether a value is a JavaScript primitive.

is.primitive(x: unknown): x is Primitive;

is.promise#

Checks whether a value is a Promise.

is.promise(x: unknown): x is Promise<unknown>;

is.request#

Checks whether a value is a Request.

is.request(x: unknown): x is Request;

is.response#

Checks whether a value is a Response.

is.response(x: unknown): x is Response;

is.regexp#

Checks whether a value is a regular expression.

is.regexp(x: unknown): x is RegExp;

is.safeint#

Checks whether a value is a safe integer number.

is.safeint(x: unknown): x is number;

is.set#

Checks whether a value is a Set.

is.set(x: unknown): x is Set<unknown>;

is.stream#

Checks whether a value is a readable web stream.

is.stream(x: unknown): x is ReadableStream;

is.string#

Checks whether a value is a string.

is.string(x: unknown): x is string;

is.symbol#

Checks whether a value is a symbol.

is.symbol(x: unknown): x is symbol;

is.text#

Checks whether a value is a nonempty, non-whitespace string.

is.text(x: unknown): x is string;

is.truthy#

Checks whether a value is truthy and narrows out falsy literals.

is.truthy<T>(
    x: T,
  ): x is Exclude<T, "" | 0 | 0n | false | null | undefined>;

is.typedarray#

Checks whether a value is an ArrayBuffer view.

is.typedarray(x: unknown): x is ArrayBufferView;

is.uint#

Checks whether a value is a non-negative integer or bigint.

is.uint(x: unknown): x is bigint | number;

is.undefined#

Checks whether a value is undefined.

is.undefined(x: unknown): x is undefined;

is.url#

Checks whether a value is a URL.

is.url(x: unknown): x is URL;

is.versioned#

Checks whether an object owns the requested global version brand.

Throws: If brand is not global or the object has another version of it.

is.versioned(x: unknown, brand: symbol): boolean;