Array methods like map(), filter(), and reduce() are very important in modern JavaScript. They help you work with arrays in a clean and readable way.

Let’s understand them with simple examples.

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1️⃣ map() – Transform Every Item

map() is used when you want to change every element in an array and return a new array.

Example: Square of numbers

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

const squares = numbers.map(num => num * num);

console.log(squares);

Output:

[1, 4, 9, 16]

How it works

• Goes through each element

• Applies a function

• Returns a new array

Visualization

[1,2,3,4]
   ↓ map
[num*num]

[1,4,9,16]

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2️⃣ filter() – Select Specific Items

filter() is used to keep only the elements that match a condition.

Example: Get even numbers

const numbers = [1,2,3,4,5,6];

const evenNumbers = numbers.filter(num => num % 2 === 0);

console.log(evenNumbers);

Output:

[2,4,6]

How it works

[1,2,3,4,5,6]
      ↓ filter
[num % 2 === 0]

[2,4,6]

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3️⃣ reduce() – Combine Values into One

reduce() is used to reduce an array into a single value.

Example: Sum of numbers

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

const sum = numbers.reduce((total, num) => total + num, 0);

console.log(sum);

Output

10

How it works

Start: 0
0 + 1 = 1
1 + 2 = 3
3 + 3 = 6
6 + 4 = 10

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4️⃣ Quick Comparison

Method	Purpose	Result
map()	Transform items	New array
filter()	Select items	New array
reduce()	Combine items	Single value

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5️⃣ Realistic Example

const users = [
  {name:"Aman", age:18},
  {name:"Riya", age:25},
  {name:"Raj", age:30}
];

const adults = users
  .filter(user => user.age >= 21)
  .map(user => user.name);

console.log(adults);

Output

["Riya","Raj"]

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✅ Memory Trick

map    → modify
filter → select
reduce → combine