12 JavaScript Code Snippets That Every Developer Must Know

JavaScript is by far the most popular language when it comes to web development. It is being used on both the client side and the server side. To improve coding efficiency, every developer should know essential JavaScript code snippets to make their development fast and easy.

1. Sorting an Array

Sorting helps organize data for better usability.

let a = [9, 3, 5, 1];
a.sort((x, y) => x - y); // Ascending
console.log(a);

a.sort((x, y) => y - x); // Descending
console.log(a);

[ 1, 3, 5, 9 ]
[ 9, 5, 3, 1 ]

• x - y sorts in ascending order, while y - x sorts in descending order.
• sort() compares elements and arranges them based on the provided function.

2. Making API Calls Using fetch()

Fetch retrieves data from a server using HTTP requests.

fetch('https://jsonplaceholder.typicode.com/users/1')
    .then(res => res.json())
    .then(data => console.log(data))
    .catch(err => console.error('Error:', err));

• fetch() makes an API call, res.json() parses the response, and catch handles errors.
• This example fetches user data and logs it to the console.

3. Find the Maximum or Minimum in an Array

Easily determine the largest or smallest number in an array.

let a = [12, 45, 7, 32];
let max = Math.max(...a);
let min = Math.min(...a);
console.log(max);
console.log(min);

45
7

• The spread operator ...a passes array elements as arguments to Math.max or Math.min.
• Math.max finds the largest number; Math.min finds the smallest.

4. Removing Duplicates from an Array

Simplify an array by keeping only unique values.

let a = [1, 2, 2, 3, 4, 4];
let unique = [...new Set(a)];
console.log(unique);

[ 1, 2, 3, 4 ]

• Set stores unique values, and ... creates a new array.
• Duplicates are automatically removed by the Set object.

5. Creating a New Array After Mapping

Transform elements of an array into a new one.

let a = [2, 4, 6];
let squared = a.map(x => x ** 2);
console.log(squared);

[ 4, 16, 36 ]

• map() applies a function (x ** 2) to each element.
• The result is a new array without modifying the original.

6. Creating a New Array After Filtering

Filter elements based on a specific condition.

let a = [10, 15, 20, 25];
let filtered = a.filter(x => x > 15);
console.log(filtered);

[ 20, 25 ]

• filter() creates a new array with elements meeting the condition.
• Here, elements greater than 15 are included.

7. Find an Element Matching a Condition

Retrieve the first element satisfying a given condition.

let a = [5, 10, 15, 20];
let found = a.find(x => x > 10);
console.log(found);

15

• find() stops and returns the first match it encounters.
• This is ideal when only one element is needed.

8. Find the Index of an Element Matching a Condition

Locate the position of an element in an array.

let a = ['apple', 'banana', 'orange'];
let idx = a.findIndex(x => x === 'banana');
console.log(idx);

• findIndex() returns the index of the first matching element.
• If no match is found, it returns -1.

9. Sum of All Elements in an Array

Add all elements of an array together.

let a = [3, 6, 9];
let sum = a.reduce((total, x) => 
	total + x, 0);
console.log(sum);

18

• reduce() accumulates values (total) while iterating through the array.
• 0 is the initial value of the accumulator.

10. Reverse a String

Reverse the characters in a string.

let s = "hello";
let rev = s.split('').reverse().join('');
console.log(rev);

olleh

• split('') converts the string into an array, reverse() reverses it, and join('') creates the reversed string.
• Ideal for palindromes or reversing text.

11. Flatten a Nested Array

Transform a multi-dimensional array into a single-level array.

let a = [1, [2, [3, 4]], 5];
let flat = a.flat(Infinity);
console.log(flat); 

[ 1, 2, 3, 4, 5 ]

• flat(Infinity) flattens all nested levels into one.
• Infinity ensures deeply nested arrays are fully flattened.

12. Clone an Array

Create a duplicate of an array.

let a = [1, 2, 3];
let clone = [...a];
console.log(clone);

[ 1, 2, 3 ]

• The spread operator ... copies all elements into a new array.
• Modifying the clone does not affect the original array.