Zefyr

Configurable and typesafe monkey patching for TypeScript.

import 'zefyr/patches';

// blueAndGreen :: ['green', 'blue']
const blueAndGreen = words('red green blue').without('red');
console.log(blueAndGreen); // ['green', 'blue']

new Date().format('yyyy-MM-dd'); // => '2023-09-01'
((3).days + (2).hours).ago() // => Date(2023-08-29T21:00:00.000Z)

const arr = [1, 2, true, 'a'];
arr.last; // => 'a'
const wrongResult = [1, 2, false].sum(); // Throws an error at runtime. wrongResult :: never
const rightResult = [1, 2, 3].sum(); // => 6. rightResult :: number

const arr2 = [1, 2, undefined, 4, null, undefined]; // arr2 :: (number | null | undefined)[]
const arr3 = arr2.compact(); // arr3 :: number[]

(54321).digits[0]; // => 1
(54321).digits(7)[1]; // => 6 (in 7-base)
-10.5.isPositive(); // => false

const obj = { a: 1, b: 2 };
const keys = Object.strictKeys(obj);
for (const key of keys) {
  console.log(obj[key]); // No type error in TypeScript
}

'hello'.reverse(); // => 'olleh'
const light = 'red' as 'red' | 'green' | 'blue' | '';
if (light.isNotEmpty()) {
  const light2 = light; // light2 :: 'red' | 'green' | 'blue'
  // ...
}

for (const n of range(3)) {
  console.log(n); // 0, 1, 2
}

Note: Zefyr requires TypeScript 5.0 or above and ES2020 or later. Currently, only ES Modules are supported.

Installation

npm

npm install zefyr

yarn

yarn add zefyr

pnpm

pnpm add zefyr

Usage

The simplest way to start using Zefyr is to import zefyr/patches in your project. It would automatically patch the global objects and prototypes, so you can use the extensions directly.

All patches are well-typed in TypeScript, as well as well-documented, you can explore them in your editor or IDE just like the built-in ones.

import 'zefyr/patches';

All patches are optional, you can import only the patches you need.

import 'zefyr/patches/Array'; // Import patches for Array
import 'zefyr/patches/Number'; // Import patches for Number
import 'zefyr/patches/Date/format'; // Import patches for only Date#format

If you dislike the Monkey Patching pattern, you can also import the patches as functions.

import { sum } from 'zefyr/Array'; // Note that `patches` is not included in the path
import isNegative from 'zefyr/Number/isNegative';

Zefyr exports a patch function for easy patching. You can create your own patches using it.

import { patch } from 'zefyr';

// Declarations are required to ensure type safety
declare global {
  interface Number {
    double(): number;
  }

  function hello(): void;
}

patch(Number).with({ double: (n) => n * 2 });
patch(globalThis).withStatic({ hello: () => console.log('Hello, world!') });

console.log((42).double()); // => 84
hello(); // => 'Hello, world!'