@alloc/is

Runtime type checking for TypeScript (inspired by @sindresorhus/is)

• isomorphic (no DOM or NodeJS types)
• type guards (for type narrowing)
• fully tested (each possible type is tested on every type checker)

Usage

First, do yarn add is@npm:@alloc/is if you never use the npm CLI. Otherwise, you need to import @alloc/is instead of is.

import { is } from 'is'

//
// Get the type name of a value.
// Object types are camel case.
//

is.what(0) // 'number'
is.what({}) // 'Object'

//
// Check the constructor of a value.
//

is.type(0, Number) // true
is.type({}, Object) // true
is.type([], Object) // false

//
// Find a constructor in a value's prototype chain.
//

is.kind([], Object) // true

//
// Check if the value is a specific type.
//

is.number(0) // true
is.array([]) // true

See the tests for expected behavior. They are very readable, just search for test( to jump between the tests of each is. function.

API

• is.what(value) Get the type name of a value
• is.type(value, constructor) Check the constructor of a value
• is.kind(value, constructor) Find a constructor in a value's prototype chain
• is.array(value) Same as Array.isArray
• is.asyncFunction(value)
• is.asyncIterable(value) Returns true for objects returned by Symbol.asyncIterator functions
• is.bigint(value)
• is.boolean(value)
• is.class(value) Returns true for class functions (but not transpiled classes)
• is.date(value)
• is.defined(value) The opposite of is.undefined
• is.emptyObject(value) Returns true for plain objects with no keys
• is.error(value)
• is.generator(value) Returns true for objects returned by generator functions
• is.generatorFunction(value)
• is.function(value)
• is.infinite(value)
• is.integer(value)
• is.iterable(value) Returns true for objects returned by Symbol.iterator functions
• is.map(value)
• is.nan(value) Same as Number.isNaN
• is.null(value)
• is.number(value) Returns true for any number (but never NaN)
• is.object(value) Returns true for any object or function (but never null)
• is.plainObject(value) Returns true for objects created by {}, new Object, or Object.create(null)
• is.promise(value)
• is.promiseLike(value) Returns true for objects with a then method
• is.regExp(value)
• is.safeInteger(value) Same as Number.isSafeInteger
• is.set(value)
• is.string(value)
• is.symbol(value)
• is.undefined(value)
• is.weakMap(value)
• is.weakSet(value)