@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.
//

isWhat(0) // 'number'
isWhat({}) // 'Object'

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

isType(0, Number) // true
isType({}, Object) // true
isType([], Object) // false

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

isKind([], Object) // true

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

isNumber(0) // true
isArray([]) // 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

• isWhat(value) Get the type name of a value
• isType(value, constructor) Check the constructor of a value
• isKind(value, constructor) Find a constructor in a value's prototype chain
• isArray(value) Same as Array.isArray
• isAsyncFunction(value)
• isAsyncIterable(value) Returns true for objects returned by Symbol.asyncIterator functions
• isBigint(value)
• isBoolean(value)
• isClass(value) Returns true for class functions (but not transpiled classes)
• isDate(value)
• isDefined(value) The opposite of isUndefined
• isEmptyObject(value) Returns true for plain objects with no keys
• isError(value)
• isGenerator(value) Returns true for objects returned by generator functions
• isGeneratorFunction(value)
• isFunction(value)
• isInfinite(value)
• isInteger(value)
• isIterable(value) Returns true for objects returned by Symbol.iterator functions
• isMap(value)
• isNan(value) Same as Number.isNaN
• isNull(value)
• isNumber(value) Returns true for any number (but never NaN)
• isObject(value) Returns true for any object or function (but never null)
• isPlainObject(value) Returns true for objects created by {}, new Object, or Object.create(null)
• isPromise(value)
• isPromiseLike(value) Returns true for objects with a then method
• isRegExp(value)
• isSafeInteger(value) Same as Number.isSafeInteger
• isSet(value)
• isString(value)
• isSymbol(value)
• isUndefined(value)
• isWeakMap(value)
• isWeakSet(value)