20 JavaScript One-Liner Functions Every Developer Should Know

Introduction

JavaScript one-liners are small utility functions that solve common problems with minimal code. They're not about being clever — they're about readability, reuse, and understanding core JavaScript concepts. This guide will show you 20 useful one-liner functions you need to know and use on any JavaScript project. All examples use modern JavaScript (ES6+) and work in both browser and Node.js environments.

If you prefer watching instead of reading, the same examples are explained step by step in the video below: Watch the video on YouTube

Number-Based One-Liners

Get a Random Number Between Two Values

const getRandomNumber = (min, max) => Math.floor(Math.random()*(max-min))+min;
 
console.log(getRandomNumber(1,10))

This function returns a random integer between min (inclusive) and max (exclusive). It's useful for things like IDs, simple games, or random selections.

Calculate the Factorial of a Number

const factorial = number => number <= 1 ? 1 : number * factorial(number - 1);
 
console.log(factorial(7))

This is a recursive one-liner that calculates the factorial of a number. Factorials are commonly used in mathematics, algorithms, and probability calculations.

Check If a Number Is Positive

const isPositive = num => num > 0;
 
console.log(isPositive(5))
console.log(isPositive(-5))

Returns true if the number is greater than zero, otherwise false.

Check If a Number Is Even

const isEven = num => num % 2 === 0;
 
console.log(isEven(1));
console.log(isEven(2));

A quick utility often used in validations and conditions.

Check If a Number Is Odd

const isOdd = num => num % 2 !== 0;
 
console.log(isOdd(2));
console.log(isOdd(3))

Returns true for odd numbers and false otherwise.

Calculate the Area of a Circle

const getCircleArea = rad => Math.PI*rad**2;
 
console.log(getCircleArea(8))

Uses the mathematical formula π × r².

Convert Celsius to Fahrenheit

const toFahrenheit = celsius => (celsius*9/5)+32;
console.log(toFahrenheit(30))

Useful for unit conversions in everyday applications.

Array-Based One-Liners

Generate a Random Item From an Array

const getRandomValue = arr => arr[Math.floor(Math.random()*arr.length)];
 
console.log(getRandomValue(["a","b","c","d","e","f","g","h"]))

This function selects a random element from an array. It works with any array type: strings, numbers, objects, or mixed values.

Shuffle an Array

const shuffle = arr => arr.sort(()=>0.5-Math.random());
 
console.log(shuffle([0,1,2,3,4,5,6,7,8,9]))

This is a simple way to shuffle an array in place.

Get Even Numbers From an Array

const getEvenNumbers = arr => arr.filter(num=>num%2===0);
 
console.log(getEvenNumbers([0,1,2,3,4,5,6,7,8,9]))

Filters out all even numbers from an array using Array.filter().

Get Odd Numbers From an Array

const getOddNumbers = arr => arr.filter(num=>num%2!==0);
 
console.log(getOddNumbers([0,1,2,3,4,5,6,7,8,9]))

The opposite of even filtering — useful for number processing tasks.

Find the Average of an Array

const getAverage = arr => (arr.reduce((acc,num)=>acc+num,0))/arr.length;
 
console.log(getAverage([0,1,2,3,4,5,6,7,8,9]))

Adds all values and divides by the array length to get the average.

Sum All Numbers in an Array

const sum = arr => arr.reduce((acc,num)=>acc+num,0);
 
console.log(sum([0,1,2,3,4,5,6,7,8,9]))

A compact way to calculate totals.

Remove Duplicates From an Array

const getUniqueItems = arr => [...new Set(arr)];
 
console.log(getUniqueItems([0,1,1,2,3,4,4,5,6,7,8,8,8,9,9,9,9,1,2,3,3,3,3,3]))

Uses Set to keep only unique values.

Check If an Array Is Empty

const isEmpty = arr => arr.length === 0;
 
console.log(isEmpty([]))
console.log(isEmpty([1,2,3]))

A simple and reliable way to check if an array contains no elements.

String-Based One-Liners

Count the Vowels in a String

const countVowels = str => (str.match(/[aeiou]/gi) || []).length;
 
console.log(countVowels("ArsenTech"))

Uses a regular expression to count vowels, ignoring case.

Reverse a String

const reverseString = str => str.split("").reverse().join("");
 
console.log(reverseString("Hello World"))

Splits the string into characters, reverses them, and joins them back.

Convert a String to an Array of Words

const toWordsArray = str => str.split(" ");
 
console.log(toWordsArray("Lorem Ipsum Dolor Sit amet"))

Splits a sentence into words using spaces as separators.

Capitalize a String

const capitalize = str => str[0].toUpperCase() + str.slice(1);
 
console.log(capitalize("arsenTech"))

Capitalizes the first character of a string.

Check If a String Is a Palindrome

const isPalindrome = str => str === str.split("").reverse().join("");
 
console.log(isPalindrome("kayak"))
console.log(isPalindrome("coding"))

A palindrome reads the same forwards and backwards. This example is case-sensitive and space-sensitive.

Things to Keep in Mind

• One-liners aren't always better If a function becomes harder to read, clarity should win over brevity.
• Some methods mutate data Functions like Array.sort() modify the original array. Clone when needed.
• Simple ≠ perfect Some shortcuts (like array shuffling) are fine for everyday use but not for cryptographic or statistical accuracy.
• Understand before copying These examples are most useful when you understand why they work, not just that they work.

Conclusion

JavaScript one-liners are small tools that solve common problems efficiently and clearly. When used thoughtfully, they can reduce boilerplate and make your code easier to read and maintain.

You don't need to memorize all of them — just recognize patterns and reuse what fits your project.

• Full Walkthrough for visual explanations: https://youtu.be/c-HgptUzl8o
• Github Gist: https://gist.github.com/ArsenTech/f9d2b599cb758c889938a8c943860a57

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