js-type-guard 🚀

Lightweight, fast, and practical type-check utilities for JavaScript and TypeScript developers. js-type-guard gives you a small set of predictable helpers to check runtime values — clear API, zero fuss, ready for production. ✨

Why choose js-type-guard? 🎯

• Minimal and focused: a compact collection of common type checks (strings, numbers, arrays, dates, regex, etc.).
• Predictable results: simple boolean utilities you can rely on in runtime guards and validation flows.
• TypeScript-friendly: shipped with TypeScript declarations so IDEs give great autocomplete and hints.
• Zero dependencies: tiny footprint, easy to audit and include in any project.

Install

npm install js-type-guard
# or
yarn add js-type-guard

Quick start — JavaScript (CommonJS)

const { isString, isArray, WTF } = require('js-type-guard');

console.log(isString('hello')); // true
console.log(isArray([1,2,3])); // true
console.log(WTF([1,2,3])); // 'array' 😄

Plain JavaScript — Node.js (require)

If you're using plain Node.js with CommonJS modules, you can require the whole module or destructure the helpers.

// destructure specific helpers
const { isString, WTF } = require('js-type-guard');

console.log(isString('hello')); // true
console.log(WTF(/abc/)); // 'regexp' 🎯

// or require the module as an object
const jsType = require('js-type-guard');
console.log(jsType.WTF(new Date())); // 'date'

Quick start — TypeScript / ESM

import { isNumber, isRegExp, WTF } from 'js-type-guard';

if (isNumber(value)) {
  // runtime check passed — value is a number at runtime
}

const rx = /abc/;
console.log(isRegExp(rx)); // true
console.log(WTF(rx)); // 'regexp' 🎯

Class usage (optional)

import { Type } from 'js-type-guard';

console.log(Type.isString('a')); // true
console.log(Type.isNull(null)); // true
console.log(Type.WTF(new Date())); // 'date'

API

| Function | Description | Returns | |---------------------|---------------------------------------------------------------------------------------------------|----------:| | isString(value) | Checks if value is a string (primitive or String object) | boolean | | isNumber(value) | Checks if value is a number (primitive or Number object) | boolean | | isBoolean(value) | Checks if value is a boolean | boolean | | isDate(value) | Checks if value is a Date instance | boolean | | isFunction(value) | Checks if value is a function | boolean | | isArray(value) | Checks if value is an Array | boolean | | isObject(value) | Checks if value is a plain Object ("[object Object]") | boolean | | isUndefined(value) | Checks if value is undefined | boolean | | isNull(value) | Checks if value is null | boolean | | isRegExp(value) | Checks if value is a RegExp instance | boolean | | isMap(value) | Checks if value is a Map instance | boolean | | isSet(value) | Checks if value is a Set instance | boolean | | isSymbol(value) | Checks if value is a Symbol | boolean | | isError(value) | Checks if value is an Error instance | boolean | | isBigInt(value) | Checks if value is a BigInt | boolean | | isArguments(value) | Checks if value is an arguments object | boolean | | isTypedArray(value) | Checks if value is a TypedArray (e.g., Int8Array, Uint8Array) | boolean | | WTF(value) | Returns the runtime type string (lowercased, e.g. 'array', 'date', 'regexp', 'null', 'undefined') | string |

Each boolean function returns whether the runtime value matches the check. WTF returns the runtime type string (lowercased) using Object.prototype.toString.call(value) for highest accuracy.

Best practices 🌟

• Use these helpers as runtime guards before performing operations that assume a certain shape or type.
• In TypeScript projects you can combine these runtime checks with type narrowing patterns — consider updating the helpers to return type predicates (value is T) for even tighter integration.

Contributing & Support 💬

Contributions, issues and feature requests are welcome. Please open an issue or a PR.

License

MIT