js-lab

A small JavaScript utility library built from scratch to learn how core language features work under the hood.

It includes:

• custom Array.prototype methods
• custom String.prototype methods
• standalone array and string helpers
• debounce/throttle performance helpers
• a simple custom iterator

This project is written in CommonJS and is designed both for learning and for experimenting with JavaScript internals.

Table of contents

• Features
• Installation
• Usage
• Modules
• API Reference
• Project Structure
• Notes
• Contributing
• License

Features

• Learn how built-in array methods work by re-implementing them yourself
• Explore string helpers and prototype methods
• Use reusable utilities for interview-style array problems
• Control event frequency with debounce and throttle
• Create custom iterators that follow the Iterator Protocol

Installation

npm install @yogesh_longwani/js-lab

Or clone the repository and work directly with the source files.

Note: this package currently exposes module subpaths like js-lab/array, js-lab/string, js-lab/performance, and js-lab/iterators.

Usage

Array utilities

const {
  applyArrayPrototypes,
  removeDuplicates,
  findMaxMin,
} = require("@yogesh_longwani/js-lab/array");

applyArrayPrototypes();

console.log([1, 2, 3].myMap((x) => x * 2));
// [2, 4, 6]

console.log(removeDuplicates([1, 2, 2, 3, 3, 4]));
// [1, 2, 3, 4]

console.log(findMaxMin([5, 9, 1, 7]));
// { min: 1, max: 9 }

String utilities

const {
  applyStringPrototypes,
  compressString,
  firstNonRepeatingChar,
} = require("@yogesh_longwani/js-lab/string");

applyStringPrototypes();

console.log("hello".myToUpperCase());
// HELLO

console.log(compressString("aaabbcccc"));
// a3b2c4

console.log(firstNonRepeatingChar("aabbcdd"));
// c

Performance helpers

const { debounce, throttle } = require("@yogesh_longwani/js-lab/performance");

const onSearch = debounce((query) => {
  console.log("Searching for:", query);
}, 300);

const onScroll = throttle(() => {
  console.log("Scroll event handled");
}, 100);

Iterator helper

const { makeIterator } = require("@yogesh_longwani/js-lab/iterators");

const iterator = makeIterator(0, 5, 2);

console.log(iterator.next());
// { value: 0, done: false }
console.log(iterator.next());
// { value: 2, done: false }
console.log(iterator.next());
// { value: 4, done: false }

Modules

js-lab/array

Contains both prototype methods and standalone array utilities.

Prototype methods

Call applyArrayPrototypes() once to attach the custom methods to Array.prototype.

Standalone utilities

Use these without modifying native prototypes.

js-lab/string

Contains custom string prototype methods plus standalone string helpers.

js-lab/performance

Contains debounce and throttle for controlling function execution rate.

js-lab/iterators

Contains a custom iterator factory built around the Iterator Protocol.

API Reference

Array prototype methods

Mutation methods

• myPush(...items) — add items to the end of an array
• myPop() — remove the last element
• myShift() — remove the first element
• myUnshift(x) — add one element to the beginning
• myReverse() — reverse an array in place
• mySplice(start, deleteCount) — custom splice implementation

Iteration methods

• myForEach(callback)
• myMap(callback)
• myFilter(callback)
• myFind(callback)
• myFindIndex(callback)
• myEvery(callback)
• mySome(callback)
• mySlice(start, end)
• myLastIndexOf(searchElement)

Standalone array utilities

• removeDuplicates(arr)
• findFirstDuplicate(arr)
• findFirstMissingNumber(arr)
• findMaxMin(arr)
• findSecondLargest(arr)
• intersection(arr1, arr2)
• isSubarray(mainArr, subArr)
• majorityElement(arr)
• moveZerosToEnd(arr)
• reverseArray(arr)
• rotateArray(arr, k)
• myConcat(...arrays)
• myJoin(arr, separator)
• isPalindrome(arr)

String prototype methods

• myToUpperCase()
• myToLowerCase()
• myIndexOf(char)

Standalone string utilities

• compressString(str)
• firstNonRepeatingChar(str)
• stringToInteger(str)

Performance helpers

• debounce(fn, delay)
• throttle(fn, delay)

Iterator helper

• makeIterator(start, end, step)

Project Structure

js-lab/
├── package.json
├── README.md
├── index.js
└── src/
    ├── array/
    │   ├── index.js
    │   ├── prototypes.js
    │   └── utils.js
    ├── string/
    │   └── index.js
    ├── performance/
    │   └── index.js
    └── iterators/
        └── index.js

Notes

• This library is great for learning and experimenting with JavaScript behavior.
• Prototype patching is optional, but it should be used carefully in real projects.
• Some methods are educational re-implementations and may not fully match every edge case of the native JavaScript methods.

Contributing

Pull requests, fixes, and improvements are welcome.

A good contribution usually includes:

• clear function names
• comments where the logic is not obvious
• examples in the README
• tests for new helpers

License

Choose a valid SPDX license identifier in package.json, such as MIT or UNLICENSED.