valid-types

A lightweight, zero-dependency JavaScript/TypeScript type-checking utility. Provides reliable type guards for all built-in JS types, including edge cases like NaN, arguments, async functions, and ES6+ types (Map, Set, Promise, Symbol, etc.).

Installation

npm install valid-types
# or
yarn add valid-types

Usage

import { isString, isNumber, isArray } from 'valid-types';

isString('hello');   // true
isNumber(42);        // true
isArray([1, 2, 3]);  // true

CommonJS is also supported:

const { isString } = require('valid-types');

API

Primitives

| Function | Description | Example | |---|---|---| | isString(value) | true for string primitives | isString('hi') → true | | isNumber(value) | true for finite numbers (excludes NaN) | isNumber(NaN) → false | | isBoolean(value) | true for true / false | isBoolean(1) → false | | isNull(value) | true only for null | isNull(null) → true | | isUndefined(value) | true only for undefined | isUndefined(undefined) → true | | isDefined(value) | true for anything except undefined | isDefined(null) → true | | isNan(value) | true only for NaN (not string "NaN") | isNan(NaN) → true | | isSymbol(value) | true for symbol primitives | isSymbol(Symbol()) → true |

Objects

| Function | Description | Example | |---|---|---| | isObject(value) | true for plain objects only (not null, Array, Date, etc.) | isObject({}) → true | | isArray(value) | true for arrays | isArray([]) → true | | isDate(value) | true for Date instances | isDate(new Date()) → true | | isRegExp(value) | true for RegExp instances | isRegExp(/abc/) → true | | isMap(value) | true for Map instances | isMap(new Map()) → true | | isSet(value) | true for Set instances | isSet(new Set()) → true | | isError(value) | true for Error and subclasses | isError(new TypeError()) → true | | isArguments(value) | true for arguments objects (not array-likes) | — |

Functions

| Function | Description | Example | |---|---|---| | isFunction(value) | true for regular and arrow functions only | isFunction(() => {}) → true | | isClass(value) | true for ES6 class declarations | isClass(class Foo {}) → true | | isAsync(value) | true for async functions (not Promise instances) | isAsync(async () => {}) → true | | isPromise(value) | true for Promise instances | isPromise(Promise.resolve()) → true |

Strings & URLs

| Function | Description | Example | |---|---|---| | isUrl(value) | true for valid http:, https:, or ftp: URLs | isUrl('https://example.com') → true | | isBase64(value) | true for base64 data URLs (data:...;base64,...) | isBase64('data:image/png;base64,abc') → true |

Empty checks

| Function | Description | Example | |---|---|---| | isEmpty(value) | true for '', 0, '0', null, false, undefined | isEmpty('') → true | | isEmptyObject(value) | true for plain objects with no own keys | isEmptyObject({}) → true | | isEmptyArray(value) | true for arrays with no elements | isEmptyArray([]) → true |

Generic

| Function | Returns | Example | |---|---|---| | isType(value) | String type name | isType(new Map()) → 'map' |

Possible return values: 'string', 'number', 'NaN', 'boolean', 'undefined', 'null', 'symbol', 'object', 'array', 'date', 'regexp', 'map', 'set', 'error', 'promise', 'function', 'class', 'async', 'arguments', 'dom', 'document'

TypeScript

All functions ship with full TypeScript support. Where possible they are typed as proper type guards:

function processInput(value: unknown) {
  if (isString(value)) {
    // value is string here
    console.log(value.toUpperCase());
  }

  if (isArray(value)) {
    // value is unknown[] here
    value.forEach(console.log);
  }
}

Development

# run tests
npm test

# build
npm run build

# lint
npm run lint

# format
npm run format

License

MIT