10 Useful JavaScript Utility Functions Every Developer Should Know

JavaScript is a versatile language, and having a set of reliable utility functions can significantly enhance development efficiency. These functions simplify common tasks, improve code readability, and reduce errors. Below, we explore ten essential JavaScript utility functions that every developer should have in their toolkit, complete with explanations and practical examples.

1.Deep Clone an Object

Creating a deep copy of an object ensures that nested objects or arrays are fully copied, preventing unintended mutations of the original data.

function deepClone(obj) {
  return JSON.parse(JSON.stringify(obj));
}

Example:

const original = { a: 1, b: { c: 2 } };
const copy = deepClone(original);
copy.b.c = 99; // original remains unchanged

2.Format Numbers with Commas

Formatting numbers for display, such as adding commas for thousands or fixing decimal places, enhances user experience.

function formatNumber(n) {
  return n.toLocaleString();
}

Example:

formatNumber(1000000); // "1,000,000"

3.Capitalize the First Letter

function capitalize(str) {
  return str.charAt(0).toUpperCase() + str.slice(1);
}

Example:

capitalize("hello world"); // "Hello world"

4.Flatten an Array

function flattenArray(arr) {
  return arr.flat(Infinity);
}

Example:

const log = debounce(() => console.log('Debounced!'), 500);
window.addEventListener('resize', log); // Logs only after 500ms of no resizing

5.Debounce a Function

function debounce(fn, delay = 300) {
  let timeout;
  return (...args) => {
    clearTimeout(timeout);
    timeout = setTimeout(() => fn(...args), delay);
  };
}

Example:

window.addEventListener('resize', debounce(() => {
  console.log('Window resized!');
}, 500));

6.Generate a Random Hex Color

function randomColor() {
  return `#${Math.floor(Math.random() * 0xffffff).toString(16).padStart(6, '0')}`;
}

Example:

randomColor(); // "#a3e12f"

7.Check If an Object is Empty

function isEmpty(obj) {
  return Object.keys(obj).length === 0;
}

Example:

isEmpty({}); // true
isEmpty({ name: 'John' }); // false

8.Convert Query String to Object

function parseQueryString(query) {
  return Object.fromEntries(new URLSearchParams(query));
}

Example:
Converts ?name=John&age=30 into a usable object.

parseQueryString('?name=John&age=30'); // { name: "John", age: "30" }

9.Copy Text to Clipboard

Splitting an array into smaller chunks is useful for pagination or batch processing.

async function copyToClipboard(text) {
  await navigator.clipboard.writeText(text);
}

Example:
Enable “copy” buttonsfor links, promo codes, etc.

copyToClipboard("Hello, world!");

Works only on HTTPSand requires user interaction in modern browsers.

10.Generate a UUID (v4-style)

function generateUUID() {
  return crypto.randomUUID();
}

Example:
Create unique IDs for form elements, DB records, or tokens.

generateUUID(); // "6fd9f51c-8df3-4a7b-a1f7-3c72ec518d1a"

Native crypto.randomUUID() is supported in all modern browsers (2022+).

Bonus: Wrap These in a Utility Module

You can group all of these into a single reusable file:

// utils.js
export {
  deepClone,
  formatNumber,
  capitalize,
  flattenArray,
  debounce,
  randomColor,
  isEmpty,
  parseQueryString,
  copyToClipboard,
  generateUUID
};

Then use them across your app:

import { debounce, formatNumber } from './utils.js';

JavaScript utility functions are more than time-savers — they make your code cleaner, safer, and easier to maintain. Whether you're building a side project, an enterprise dashboard, or contributing to open source, mastering these functions gives you a real productivity boost.

Tip: Avoid rewriting the wheel on large projects. Use libraries like Lodash, Ramda, or Rambdawhen your app grows.