Santi's Assertion Library

• 🚀 Lightweight and fast^
• 👴 ES3-compliant*
• 💻 Portable between the browser and Node.js
• 📘 Comes with built-in TypeScript definitions
• 📑 Split into a lot of modules (under cjs/) so you get to choose what you want
• 🎨 Includes a wide array of assertion functions
• 💪 Very customizable (you get to choose comparison logic, name displayed on error, et cetera)

*Hasn't been tested in an actual ES3 environment. Feel free to open an issue or pull request if you find any non-ES3 thing. See "Contribute" for instructions on how to do so.

^The source code is about 2 kilobytes.

What's this?

This is an assertion library for types and conditions. It's designed to be lightweight and portable between the browser and Node.js.

Contribute

Wanna contribute? File an issue or pull request! Make sure you follow the contribution Code of Conduct.

Installation

• Via NPM: npm install @santi100/assertion-lib
• Via Yarn: yarn add @santi100/assertion-lib
• Via PNPM: pnpm install @santi100/assertion-lib

API

• function assert(condition: boolean, params?: AssertOptionalParams): void;

  Asserts that condition is truthy. Throws an AssertionError otherwise.

  Parameter	Type	Description
  condition	boolean	The condition to assert.
  assertParams	AssertOptionalParams<E, A>	AssertionError options.
  assertParams.expected	E	Expected value for the assertion.
  assertParams.actual	A	Received value for the assertion.
  assertParams.operator	string	Optional operator used for the assertion.

• function assertTypeOf(arg: any, expectedType: Type, name: string): void; (since 1.0.6, name is optional since 1.0.8)

  Asserts that the type of arg is expectedType. Throws a TypeError otherwise.

  Parameter	Type	Description
  arg	any	An expression whose type is to be asserted.
  expectedType	Type	The expected type.
  name	string	An optional expression name to be put in the TypeError's message. Defaults to "arg".

• function assertOneOf<T = unknown>(arg: any, name: string, choices: any[]): void; (since 1.0.6, type param bound to choices added in 1.0.8)

  Asserts arg is one of choices, using comparator to compare arg against each choice. Throws a TypeError otherwise.

  WARNING: Since v2, the shallow argument is no longer valid -- it has been replaced with comparator.

  This is done so you can use this library without the need to install @santi100/equal-lib, whilst also adding flexibility to use custom comparison logic or the deep equality library of your choice.

  Parameter	Type	Description
  arg	any	The value that's expected to be included within choices.
  name	string	An expression name to be put in the TypeError's message.
  choices	T[]	An array containing the posible values arg should have in order for an error not to be thrown.
  comparator? (since 2.0.0)	(a: unknown, b: T) => boolean or undefined	A custom comparator to add, for instance, deep equality!

• function assertInteger(arg: number, name: string): void; (since 1.0.6)

  Asserts arg is an integer. Throws a TypeError otherwise.

• function assertMin(arg: any, name: string, min: any): void; (since 1.0.6)

  Asserts arg is bigger or equal than min. Throws a TypeError otherwise.

• function assertMax(arg: any, name: string, max: any): void; (since 1.0.6)

  Asserts arg is smaller or equal than max. Throws a TypeError otherwise.

• function assertRange(arg: any, name: string, min: any, max: any): void; (since 1.0.6)

  Asserts arg is NEITHER smaller than min NOR bigger than max. Throws a TypeError (RangeError since 1.0.7) otherwise.

• function assertArray(arg: any, name?: string): void; (since 1.0.7)

  Asserts arg is an Array. Throws a TypeError otherwise.

• function assertDefined<T = unknown>(element: T): void; (since 2.0.1)

  Checks if a given element is defined, i.e., not null or undefined. If the element is null or undefined, the function throws a TypeError with a message indicating the name of the element.

  Parameter	Type	Description	Optional?
  element	T	The value to be checked for being defined.	No

  Throws an error if the element is null or undefined.

  Example:

  assertDefined(5); // No error thrown
  assertDefined(null); // Throws TypeError: 'element' is null
  assertDefined(undefined); // Throws TypeError: 'element' is undefined
  assertDefined('hello'); // No error thrown

• function assertMatch(str: string, re: RegExp, name?: string): void; (since 2.0.1)

  Asserts str matches re. Throws a TypeError otherwise.

  Parameter	Type	Description	Optional?
  str	string	The string to match against re.	No
  re	RegExp	The regular expression to match str against.	No
  name	string	The displayed name in the TypeError thrown if str does not match re.
  Defaults to str.	No

Usage example

// Import the assertion functions

// CJS
const assert = require('@santi100/assertion-lib/cjs/assert');
const assertTypeOf = require('@santi100/assertion-lib/cjs/type-of');
const assertOneOf = require('@santi100/assertion-lib/cjs/one-of');
const assertInteger = require('@santi100/assertion-lib/cjs/integer');
const assertMin = require('@santi100/assertion-lib/cjs/min');
const assertMax = require('@santi100/assertion-lib/cjs/max');
const assertRange = require('@santi100/assertion-lib/cjs/range');
const assertArray = require('@santi100/assertion-lib/cjs/array');
const assertDefined = require('@santi100/assertion-lib/cjs/defined');
const assertMatch = require('@santi100/assertion-lib/cjs/match');

// TypeScript
import assert = require('@santi100/assertion-lib/cjs/assert');
import assertTypeOf = require('@santi100/assertion-lib/cjs/type-of');
import assertOneOf = require('@santi100/assertion-lib/cjs/one-of');
import assertInteger = require('@santi100/assertion-lib/cjs/integer');
import assertMin = require('@santi100/assertion-lib/cjs/min');
import assertMax = require('@santi100/assertion-lib/cjs/max');
import assertRange = require('@santi100/assertion-lib/cjs/range');
import assertArray = require('@santi100/assertion-lib/cjs/array');
import assertDefined = require('@santi100/assertion-lib/cjs/defined');
import assertMatch = require('@santi100/assertion-lib/cjs/match');

// ESM
import assert from '@santi100/assertion-lib/cjs/assert';
import assertTypeOf from '@santi100/assertion-lib/cjs/type-of';
import assertOneOf from '@santi100/assertion-lib/cjs/one-of';
import assertInteger from '@santi100/assertion-lib/cjs/integer';
import assertMin from '@santi100/assertion-lib/cjs/min';
import assertMax from '@santi100/assertion-lib/cjs/max';
import assertRange from '@santi100/assertion-lib/cjs/range';
import assertArray from '@santi100/assertion-lib/cjs/array';
import assertDefined from '@santi100/assertion-lib/cjs/defined';
import assertMatch from '@santi100/assertion-lib/cjs/match';

// Or import it all
import * as assertionLib from '@santi100/assertion-lib'; // ESM or TypeScript
const assertionLib = require('@santi100/assertion-lib'); // CJS
// Usage example for assert
function divide(a, b) {
  assert(typeof a === 'number' && typeof b === 'number', {
    message: 'Arguments must be numbers.'
  });

  assert(b !== 0, {
    message: 'Cannot divide by zero.',
    expected: 'Non-zero value',
    actual: b
  });

  return a / b;
}

// Usage example for assertTypeOf
function greet(name) {
  assertTypeOf(name, 'string', 'name');

  return `Hello, ${name}!`;
}

// Usage example for assertOneOf
function checkOperator(operator) {
  assertOneOf(operator, 'operator', ['+', '-', '*', '/'], (a, b) => a.trim() === b.trim());
  return `Valid operator: ${operator}`;
}

// Usage example for assertInteger
function multiplyByTwo(num) {
  assertInteger(num, 'num');
  return num * 2;
}

// Usage example for assertMin
function greetWithMinimumLength(name) {
  assertMin(name.length, 'name', 3);
  return `Hello, ${name}!`;
}

// Usage example for assertMax
function greetWithMaximumLength(name) {
  assertMax(name.length, 'name', 10);
  return `Hello, ${name}!`;
}

// Usage example for assertRange
function greetWithPreferredLength(name) {
  assertRange(name.length, 'name', 5, 8);
  return `Hello, ${name}!`;
}

// Usage example for assertArray
function sumNumbers(numbers) {
  assertArray(numbers, 'numbers');
  return numbers.reduce((sum, num) => sum + num, 0);
}

// Usage example for assertDefined
function greetIfDefined(name) {
  assertDefined(name, 'name');
  return `Hello, ${name}!`;
}

// Usage example for assertMatch
function isValidEmail(email) {
  assertMatch(email, /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/i, 'email');
  return true;
}