Array Methods in JavaScript: Built-in Functions

JavaScript provides an array of built-in methods that simplify and enhance common operations on arrays. Let’s explore some of these methods to level up your array manipulation skills.

1. forEach: Execute a Function for Each Element

The forEach method allows you to iterate over each element in an array and execute a provided function:

const numbers = [1, 2, 3, 4, 5];

numbers.forEach((number, index) => {
  console.log(`Element at index ${index}: ${number}`);
// Output:
// Element at index 0: 1
// Element at index 1: 2
// Element at index 2: 3
// Element at index 3: 4
// Element at index 4: 5

2. map: Transform Array Elements

The map method creates a new array by applying a function to each element of the original array:

const squares = => number * number);
console.log(squares); // Output: [1, 4, 9, 16, 25]

3. filter: Create a New Array with Filtered Elements

The filter method creates a new array containing only elements that satisfy a provided condition:

const evens = numbers.filter(number => number % 2 === 0);
console.log(evens); // Output: [2, 4]

4. reduce: Reduce Array to a Single Value

The reduce method applies a function against an accumulator and each element in the array to reduce it to a single value:

const sum = numbers.reduce((accumulator, number) => accumulator + number, 0);
console.log(sum); // Output: 15

5. some and every: Check Array Elements

The some method checks if at least one element satisfies a condition, while every checks if all elements satisfy a condition:

const hasEven = numbers.some(number => number % 2 === 0);
console.log(hasEven); // Output: true

const allEven = numbers.every(number => number % 2 === 0);
console.log(allEven); // Output: false

6. indexOf and lastIndexOf: Find Element Index

indexOf returns the first index at which a given element can be found, and lastIndexOf returns the last index:

const index = numbers.indexOf(3);
console.log(index); // Output: 2

const lastIndex = numbers.lastIndexOf(3);
console.log(lastIndex); // Output: 2


Built-in array methods in JavaScript provide a concise and expressive way to perform common operations on arrays. Whether you’re transforming elements, filtering based on conditions, or reducing arrays to single values, these methods empower you to write cleaner and more efficient code.

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