@fabiospampinato/is

Is

The definitive collection of is* functions for runtime type checking. Lodash-compatible, tree-shakable, with types.

Features

• Lodash-compatible: The provided functions are compatible with lodash's, so they can be used as drop-in replacements. This includes non-obvious things like being able to work with polyfilled builtins, not throwing in old environments where things like Map aren't available, working with objects from other realms, working with weird things like Boolean ( true ) and Object ( true ), and being isomorphic.
• Types: Good TypeScript types ship with the library rather than being an afterthought. Also more subtlety this means that some extra functions like isFalsy and isTruthy are provided because their return type is useful for type checking, for lodash it doesn't make much sense to provide these functions because all their value is in the type system, and lodash doesn't care about that.
• Modern: Some functions have been updated to account for bigints and some addititional ones have been added, the library is tree-shakable so you only pay for what you use.
• Focused: Every function provided accepts a single argument of unknown type and returns a boolean, almost always as a TypeScript type guard.

Install

npm install --save is@npm:@fabiospampinato/is

Usage

isArguments

Checks if a value is an arguments object.

import {isArguments} from 'is';

const args = (function () { return arguments; })();

isArguments ( args ); // => true
isArguments ( [] ); // => false

isArrayBuffer

Checks if a value is an ArrayBuffer object.

import {isArrayBuffer} from 'is';

isArrayBuffer ( new ArrayBuffer ( 8 ) ); // => true
isArrayBuffer ( [] ); // => false

isArrayLikeObject

Checks if a value is an Array-like object, meaning a non-string and non-function with an integer length property.

import {isArrayLikeObject} from 'is';

isArrayLikeObject ( [] ); // => true
isArrayLikeObject ( { length: 1 } ); // => true
isArrayLikeObject ( 'foo' ); // => false
isArrayLikeObject ( isArrayLikeObject ); // => false

isArrayLike

Checks if a value is an Array-like object, meaning a non-function with an integer length property.

import {isArrayLike} from 'is';

isArrayLike ( [] ); // => true
isArrayLike ( { length: 1 } ); // => true
isArrayLike ( 'foo' ); // => true
isArrayLike ( isArrayLike ); // => false

isArray

Checks if a value is an Array.

import {isArray} from 'is';

isArray ( [] ); // => true
isArray ( {} ); // => false

isBigInt 🆕

Checks if a value is a BigInt.

import {isBigInt} from 'is';

isBigInt ( 0n ); // => true
isBigInt ( 0 ); // => false

isBoolean

Checks if a value is a boolean.

import {isBoolean} from 'is';

isBoolean ( true ); // => true
isBoolean ( false ); // => true
isBoolean ( 0 ); // => false;

isBuffer

Checks if a value is a Buffer.

import {isBuffer} from 'is';

isBuffer ( Buffer.from ( '' ) ); // => true
isBuffer ( [] ); // => false

isDate

Checks if a value is a Date.

import {isDate} from 'is';

isDate ( new Date () ); // => true
isDate ( 0 ); // => false

isElement

Checks if a value is likely a DOM element.

import {isElement} from 'is';

isElement ( body ); // => true
isElement ( window ); // => false

isEmpty

Checks if a value is an empty array, string, buffer, typed array, arguments object, map, set, prototype or regular object.

import {isEmpty} from 'is';

isEmpty ( [] ); // => true
isEmpty ( {} ); // => true
isEmpty ( 123 ); // => true
isEmpty ( [123] ); // => false

isError

Checks if a value is an Error.

import {isError} from 'is';

isError ( new Error () ); // => true
isError ( { message: 'asd' } ); // => false

isFalsy 🆕

Checks if a value is falsy.

import {isFalsy} from 'is';

isFalsy ( 0 ); // => true
isFalsy ( '' ); // => true
isFalsy ( [] ); // => false

isFinite

Checks if a value is a finite number.

import {isFinite} from 'is';

isFinite ( 0 ); // => true
isFinite ( Infinity ); // => false
isFinite ( -Infinity ); // => false
isFinite ( NaN ); // => false

isFloat 🆕

Checks if a value is a float.

import {isFloat} from 'is';

isFloat ( 1.2 ); // => true
isFloat ( 0 ); // => false
isFloat ( -1 ); // => false

isFunction

Checks if a value is a function.

import {isFunction} from 'is';

isFunction ( isFunction ); // => true
isFunction ( { call: () => {} } ); // => false

isInteger

Checks if a value is an integer.

import {isInteger} from 'is';

isInteger ( 0 ); // => true
isInteger ( -1 ); // => true
isInteger ( 1.2 ); // => false

isLength

Checks if a value could be a valid length index.

import {isLength} from 'is';

isLength ( 0 ); // => true
isLength ( -1 ); // => false
isLength ( 1.2 ); // => false
isLength ( Infinity ); // => false

isMap

Checks if a value is a Map.

import {isMap} from 'is';

isMap ( new Map () ); // => true
isMap ( {} ); // => false

isNaN

Checks if a value is exactly NaN.

import {isNaN} from 'is';

isNaN ( NaN ); // => true
isNaN ( undefined ); // => false

isNative

Checks if a value is likely a native function.

import {isNative} from 'is';

isNative ( [].push ); // => true
isNative ( isNative ); // => false

isNil

Checks if a value is null or undefined.

import {isNil} from 'is';

isNil ( null ); // => true
isNil ( undefined ); // => true
isNil ( {} ); // => false

isNull

Checks if a value is null.

import {isNull} from 'is';

isNull ( null ); // => true
isNull ( undefined ); // => false

isNumber

Checks if a value is a number.

import {isNumber} from 'is';

isNumber ( 0 ); // => true
isNumber ( Infinity ); // => true
isNumber ( -Infinity ); // => true
isNumber ( NaN ); // => true
isNumber ( '0' ); // => false

isObjectLike

Checks if a value is an object (not necessarily a plain object).

import {isObjectLike} from 'is';

isObjectLike ( {} ); // => true
isObjectLike ( [] ); // => true
isObjectLike ( isObjectLike ); // => false

isObject

Checks if a value is not a primitive. This is the opposite of isPrimitive.

import {isObject} from 'is';

isObject ( {} ); // => true
isObject ( [] ); // => true
isObject ( isObject ); // => true
isObject ( 123 ); // => false

isPlainObject

Checks if a value is a plain object.

import {isPlainObject} from 'is';

isPlainObject ( {} ); // => true
isPlainObject ( [] ); // => false
isPlainObject ( isPlainObject ); // => false

isPrimitive 🆕

Checks if a value is a primitive. This is the opposite of isObject.

import {isPrimitive} from 'is';

isPrimitive ( null ); // => true
isPrimitive ( undefined ); // => true
isPrimitive ( '' ); // => true
isPrimitive ( 0 ); // => true
isPrimitive ( 0n ); // => true
isPrimitive ( true ); // => true
isPrimitive ( Symbol () ); // => true
isPrimitive ( {} ); // => false
isPrimitive ( isPrimitive ); // => false

isPromise 🆕

Checks if a value is a Promise.

import {isPromise} from 'is';

isPromise ( Promise.resolve () ); // => true
isPromise ( Promise.reject () ); // => true
isPromise ( { then: () => {} } ); // => false

isPrototype 🆕

Checks if a value is likely a prototype.

import {isPrototype} from 'is';

isPrototype ( Array.prototype ); // => true
isPrototype ( isPrototype ); // => false

isRegExp

Checks if a value is likely a regex.

import {isRegExp} from 'is';

isRegExp ( /x/ ); // => true
isRegExp ( new RegExp ( 'x' ) ); // => true
isRegExp ( 'x' ); // => false

isSafeInteger

Checks if a value is an integer that can be represented faithfully in JavaScript.

import {isSafeInteger} from 'is';

isSafeInteger ( 0 ); // => true
isSafeInteger ( Number.MAX_SAFE_INTEGER ); // => true
isSafeInteger ( -Number.MAX_SAFE_INTEGER ); // => true
isSafeInteger ( Number.MAX_SAFE_INTEGER + 1 ); // => false

isSet

Checks if a value is a Set.

import {isSet} from 'is';

isSet ( new Set () ); // => true
isSet ( [] ); // => false

isString

Checks if a value is a string.

import {isString} from 'is';

isString ( 'foo' ); // => true
isString ( ['f', 'o', 'o'] ); // => false

isSymbol

Checks if a value is a symbol.

import {isSymbol} from 'is';

isSymbol ( Symbol () ); // => true
isSymbol ( {} ); // => false

isTruthy

Checks if a value is truthy.

import {isTruthy} from 'is';

isTruthy ( [] ); // => true
isTruthy ( 0 ); // => false
isTruthy ( '' ); // => false

isTypedArray

Checks if a value is a TypedArray.

import {isTypedArray} from 'is';

isTypedArray ( new Int8Array ( 8 ) ); // => true
isTypedArray ( [] ); // => false

isUndefined

Checks if a value is undefined.

import {isUndefined} from 'is';

isUndefined ( undefined ); // => true
isUndefined ( null ); // => false

isWeakMap

Checks if a value is a WeakMap.

import {isWeakMap} from 'is';

isWeakMap ( new WeakMap () ); // => true
isWeakMap ( new Map () ); // => false

isWeakSet

Checks if a value is a WeakSet.

import {isWeakSet} from 'is';

isWeakSet ( new WeakSet () ); // => true
isWeakSet ( new Set () ); // => false

License

• Parts: MIT © Fabio Spampinato.
• Parts: MIT © lodash.