is-check-js

A comprehensive utility library for type checking and validation in Node.js and JavaScript applications.

Features

• Comprehensive Type Checking: Over 30 utility functions for type validation
• TypeScript Support: Full TypeScript definitions included
• Zero Dependencies: Lightweight with no external dependencies
• Well Tested: 100% test coverage with Jest
• Modern JavaScript: Supports all modern JavaScript types including BigInt and Symbol
• Advanced Validations: Email, URL, IP address, credit card, and more

Installation

yarn add is-check-js

Quick Start

import { isString, isEmail, isEmpty, isPositive } from 'is-check-js';

// Basic type checking
console.log(isString('hello')); // true
console.log(isString(123)); // false

// Advanced validation
console.log(isEmail('[email protected]')); // true
console.log(isEmpty('')); // true
console.log(isPositive(5)); // true

API Reference

Basic Type Checking

isString(value)

Check if value is a string.

isString('hello'); // true
isString(123); // false

isNumber(value)

Check if value is a number (excluding NaN).

isNumber(123); // true
isNumber('123'); // false
isNumber(NaN); // false

isBoolean(value)

Check if value is a boolean.

isBoolean(true); // true
isBoolean('true'); // false

isFunction(value)

Check if value is a function.

isFunction(() => {}); // true
isFunction(Math.max); // true

isArray(value)

Check if value is an array.

isArray([]); // true
isArray([1, 2, 3]); // true
isArray({}); // false

isObject(value)

Check if value is a plain object (not array, null, or other objects).

isObject({}); // true
isObject({ a: 1 }); // true
isObject([]); // false
isObject(null); // false

isObjectLike(value)

Check if value is any type of object (including arrays, dates, etc.).

isObjectLike({}); // true
isObjectLike([]); // true
isObjectLike(new Date()); // true
isObjectLike(null); // false

isDate(value)

Check if value is a valid Date object.

isDate(new Date()); // true
isDate(new Date('invalid')); // false

isRegExp(value)

Check if value is a RegExp object.

isRegExp(/test/); // true
isRegExp(new RegExp('test')); // true

isNull(value), isUndefined(value), isNil(value)

Check for null, undefined, or both.

isNull(null); // true
isUndefined(undefined); // true
isNil(null); // true
isNil(undefined); // true

isSymbol(value), isBigInt(value)

Check for modern JavaScript types.

isSymbol(Symbol('test')); // true
isBigInt(123n); // true

Advanced Validation

isEmpty(value)

Check if value is empty (works with strings, arrays, objects, Maps, Sets).

isEmpty(''); // true
isEmpty([]); // true
isEmpty({}); // true
isEmpty(null); // true
isEmpty('hello'); // false

isEmail(value)

Validate email addresses.

isEmail('[email protected]'); // true
isEmail('invalid-email'); // false

isURL(value)

Validate URLs.

isURL('https://example.com'); // true
isURL('http://localhost:3000'); // true
isURL('not-a-url'); // false

isPhoneNumber(value)

Basic phone number validation.

isPhoneNumber('1234567890'); // true
isPhoneNumber('+1 (555) 123-4567'); // true

isJSON(value)

Check if string is valid JSON.

isJSON('{"name": "John"}'); // true
isJSON('{invalid}'); // false

Number Validation

isPositive(value), isNegative(value), isZero(value)

Number sign validation.

isPositive(5); // true
isNegative(-3); // true
isZero(0); // true

isInteger(value), isFloat(value)

Number type validation.

isInteger(42); // true
isFloat(3.14); // true

isEven(value), isOdd(value)

Even/odd number validation.

isEven(4); // true
isOdd(3); // true

isInRange(value, min, max)

Check if number is within a range.

isInRange(5, 0, 10); // true
isInRange(15, 0, 10); // false

Advanced Format Validation

isCreditCard(value)

Validate credit card numbers using Luhn algorithm.

isCreditCard('4111111111111111'); // true (Visa test number)

isIPv4(value), isIPv6(value)

IP address validation.

isIPv4('192.168.1.1'); // true
isIPv6('2001:0db8:85a3:0000:0000:8a2e:0370:7334'); // true

isHexColor(value)

Hexadecimal color validation.

isHexColor('#ff5733'); // true
isHexColor('#fff'); // true

isUUID(value)

UUID validation.

isUUID('123e4567-e89b-12d3-a456-426614174000'); // true

Utility Functions

isAny(value, ...predicates)

Check if value matches any of the provided predicates.

isAny('hello', isString, isNumber); // true
isAny(123, isString, isNumber); // true

isAll(value, ...predicates)

Check if value matches all of the provided predicates.

isAll('hello', isString, v => v.length > 0); // true

isType(value, type)

Check if value is of a specific type using string comparison.

isType('hello', 'string'); // true
isType([], 'array'); // true
isType(null, 'null'); // true

isTruthy(value), isFalsy(value)

Check truthiness and falsiness.

isTruthy(1); // true
isFalsy(0); // true

getType(value)

Get the type of a value as a string.

getType('hello'); // 'string'
getType([]); // 'array'
getType(null); // 'null'
getType(new Date()); // 'date'

TypeScript Support

The library includes comprehensive TypeScript definitions:

import { isString, isEmail, isEmpty } from 'is-check-js';

const userInput: unknown = getUserInput();

if (isString(userInput)) {
  // TypeScript knows userInput is a string here
  console.log(userInput.toUpperCase());
}

if (isEmail(userInput)) {
  // TypeScript knows userInput is a string (email)
  sendEmail(userInput);
}

Testing

Run the test suite:

yarn test

# Run with coverage
yarn test:coverage

# Run in watch mode
yarn test:watch

Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Add tests for your changes
4. Ensure all tests pass (yarn test)
5. Commit your changes (git commit -m 'Add some amazing feature')
6. Push to the branch (git push origin feature/amazing-feature)
7. Open a Pull Request

License

MIT License - see the LICENSE file for details.

Changelog

1.0.0

• Initial release with comprehensive type checking and validation utilities
• TypeScript support
• Full test coverage
• Zero dependencies