⚙️ Core Higher-Order Array Methods in JavaScript

Last Updated: 22nd October 2025

Higher-Order Functions are functions that take another function as an argument (called a callback) or return a function.
In arrays, these built-in methods help to iterate, transform, or reduce data efficiently — without writing loops manually.

Hinglish Tip 🗣: Ye methods “smart loops” ki tarah kaam karte hain — aapko for ya while likhne ki zarurat nahi hoti, sab kuch ek line me ho jaata hai!

forEach() — Simple Loop for Action

Executes a function once for each element in the array.

Syntax

array.forEach(function (currentValue, index, array) {
  // code to execute
});

let fruits = ["apple", "banana", "cherry"];
fruits.forEach(function (item, index) {
  console.log(index + ": " + item);
});

// Output:
// 0: apple
// 1: banana
// 2: cherry

map() — Loop for Transformation

Creates a new array by applying a function to each element of the original.

Syntax

array.map(function (currentValue, index, array) {
  return newValue;
});

let numbers = [1, 2, 3];
let doubled = numbers.map((num) => num * 2);
console.log(doubled);

// Output: [2, 4, 6]

filter() — Select Elements Matching Condition

Returns a new array containing only elements that satisfy a condition.

Syntax

array.filter(function (currentValue, index, array) {
  return condition; // true or false
});

let marks = [85, 42, 77, 90, 58];
let passed = marks.filter((score) => score >= 60);
console.log(passed);

// Output: [85, 77, 90]

reduce() — Combine All Values into One

Used to accumulate all elements into a single value (sum, average, etc.)

Syntax

array.reduce(function (accumulator, currentValue, index, array) {
  return updatedAccumulator;
}, initialValue);

let numbers = [1, 2, 3, 4, 5];
let sum = numbers.reduce((acc, num) => acc + num, 0);
console.log(sum);

// Output: 15

find() — Find First Element Matching Condition

Returns the first element that satisfies the condition, otherwise undefined.

Syntax

array.find(function (currentValue, index, array) {
  return condition;
});

let ages = [12, 18, 25, 30];
let adult = ages.find((age) => age >= 18);
console.log(adult);

// Output: 18

findIndex() — Find Index of First Element Matching Condition

Returns the index of the first element that satisfies the given condition.If no match is found, it returns -1.

let nums = [10, 25, 30, 45];
let index = nums.findIndex((num) => num > 20);
console.log(index);

// Output: 2

some() — Check if Any Element Satisfies Condition

Returns true if at least one element satisfies the condition, otherwise false.

let scores = [45, 60, 33, 90];
let hasPassed = scores.some((score) => score >= 50);
console.log(hasPassed);

// Output: true

every() — Check if All Elements Satisfy Condition

Returns true if all elements satisfy the condition, otherwise false.

let marks = [70, 80, 90];
let allPassed = marks.every((score) => score >= 60);
console.log(allPassed);

// Output: true

sort() — Sort Elements in an array

Sorts array elements in place (modifies original array).By default, it sorts elements as strings, not numbers!

1: Sorting Strings

let fruits = ["banana", "apple", "cherry"];
fruits.sort();
console.log(fruits);

// Output: ["apple", "banana", "cherry"]

2: Sorting Numbers

let numbers = [100, 25, 9];
numbers.sort((a, b) => a - b);
console.log(numbers);

// Output: [9, 25, 100]

Hinglish Tip 🗣: sort() bina compare function ke string sort karta hai “25” ko “100” se bada samjhta hai!

flat() — Flatten Nested Arrays

Flattens nested arrays up to a given depth.

let matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];

let flattened = matrix.flat();
console.log(flattened);

// Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

Hinglish Tip 🗣: flat() nested array ko “seedha” bana deta hai — jaise folders ke andar folder ko ek saath khol do.

flatMap() — Flatten Nested Arrays with Mapping

First applies a map function, then flattens the result by one level.

let nums = [1, 2, 3];
let result = nums.flatMap(x => [x, x * 2]);
console.log(result);

// Output: [1, 2, 2, 4, 3, 6]

💡 Quick Practice

  • Use map() to convert all temperatures from Celsius to Fahrenheit.
  • Use filter() to remove words shorter than 4 letters.
  • Use reduce() to find the average of [10, 20, 30, 40].
  • Use find() to get the first negative number in [5, -3, 7, -1].
  • Use some() to check if any element is divisible by 5.
  • Use every() to check if all ages are above 18.
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