21 Must Have JavaScript One Liners

Hi guys, in this post, I'm going to introduce JavaScript one liners that make you better JavaScript developer as they are very useful in most practical cases

1. Reverse a string

const reverseString = (str) => str.split("").reverse().join("");
console.log(reverseString("hello guys!"));
// !syug olleh

2. Flatten an array

const flattenArray = (arr, flattenLevel = 1) => arr.flat(flattenLevel);
console.log(flattenArray([1, 2, [3, 4]]));
// [1,2,3,4]
console.log(flattenArray([1, 2, [3, 4, [5]]], 2));
// [1,2,3,4, 5]

3. Shuffle an array

const shuffleArray = (arr) => arr.sort((a, b) => 0.5 - Math.random());
console.log(shuffleArray([1, 2, 3, 4, 5]));
// [2, 5, 4, 1, 3]

4. Get a random boolean value

const getRandomBooleanValue = () => Math.random() >= 0.5;
console.log(getRandomBooleanValue());
// false
console.log(getRandomBooleanValue());
// true

5. Find an average array value

const getAverageValue = (numbers) =>
  numbers.reduce((total, currEl) => total + currEl, 0) / numbers.length;
console.log(getAverageValue([1, 2, 3, 4]));
// 2.5
console.log(getAverageValue([100, 900]));
// 500

6. Detect a dark mode

const darkMode = window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches;

7. Scroll to the top of the page

const scrollToTop =() => window.scrollTo({top: 0, behavior: 'smooth'});

8. Find number of specified character in a string

const getCharAmount = (string, char) => string.split(char).length - 1;
console.log(getCharAmount("hello", "l"));
// 2
console.log(getCharAmount("hello", "q"));
// 0

9. Redirect URL

const redirectUrl = url => location.href = url;
redirectUrl("https://youtube.com");

10. Detect whether an array is empty

const isArrayEmpty = (arr) => !Array.isArray(arr) || !arr.length;
console.log(isArrayEmpty([1, 2]));
// false
console.log(isArrayEmpty([]));
// true

11. Return unique values from an array

const getUniqueArrayValues = (arr) =>
  arr.filter((i) => arr.indexOf(i) === arr.lastIndexOf(i));
console.log(getUniqueArrayValues([1, 2, 2, 3]));
// [1, 2, 3]

12. Get a selected text from DOM

const getSelectedText = () => window.getSelection().toString();

13. Check whether expression is an array

const isArray = (expression) => Array.isArray(expression);
console.log(isArray(1));
// false
console.log(isArray({ name: "Jaxongir" }));
// false
console.log(isArray(["JavaScript"]));
// false

14. Check a number if it's odd or even

const isOdd = (number) => number % 2 === 1;
console.log(isOdd(1));
// true
console.log(isOdd(2));
// false

15. Detect whether an element is in focus

const isElementFocussed = (element) => element === document.activeElement;

16. Convert celsius to fahrenheit and vice versa

const convertCelsiusToFahrenheit = (celsius) =>
  Math.floor((celsius * 9) / 5 + 32);
const convertFahrenheitToCelsius = (fahrenheit) =>
  Math.floor((fahrenheit - 32) * (5 / 9));

console.log(convertCelsiusToFahrenheit(21));
// 69
console.log(convertCelsiusToFahrenheit(-50));
// -58

console.log(convertFahrenheitToCelsius(33));
// 0
console.log(convertFahrenheitToCelsius(22));
// -6

17. Check if two arrays are the same

const isArraysTheSame = (arr1, arr2) =>
  arr1.length === arr2.length &&
  arr1.every((val, index) => val === arr2[index]);
console.log(isArraysTheSame([1, 2], [1, 2]));
// true
console.log(isArraysTheSame([1, 2], [1, 3]));
// false

18. Convert first character to an uppercase

const convertFirstCharToUppercase = (str) =>
  `${str[0].toUpperCase()}${str.slice(1)}`;
console.log(convertFirstCharToUppercase("jaxongir"));
// Jaxongir

19. Converting 24-hour clock to 12-hour clock

const convert24hTo12h = (hour) =>
  `${hour % 12 === 0 ? 12 : hour % 12}${hour > 23 || hour < 12 ? "am" : "pm"}`;
console.log(convert24hTo12h(1));

20. Replace character of string with another character

const replaceStringCharacter = (str, char) => str.replace(/e/i, char);
console.log(replaceStringCharacter("geat", "re"));
// great

21. Remove undefined or null from an array

const removeNullAndUndefined = (arr) =>
  arr.filter((val) => val != null || val != undefined);
console.log(removeNullAndUndefined([1, null, undefined, 4]));
// [1, 4]