Higher-Order Functions & Callbacks

Higher-Order Functions (HOFs) and Callback Functions — theory and examples.

Example 1 — Function as Argument (Callback)

Passing a function as an argument and executing it inside another function.

// greet callback
function greet(name) {
  return `Hello, ${name}!`;
}
function processUser(name, callback) {
  return callback(name);
}
processUser('Alice', greet);

Example 2 — Function Returning Another Function

createMultiplier returns a new function customized by multiplier.

function createMultiplier(multiplier) {
  return function(number) {
    return number * multiplier;
  };
}
const double = createMultiplier(2);
const triple = createMultiplier(3);
`double(5) → ${double(5)}; triple(5) → ${triple(5)}`;

Example 3 — map(), filter(), reduce()

Common HOFs for array transformations & aggregation.

const cart = [100, 200, 300];
const discounted = cart.map(p => p * 0.9);
const total = discounted.reduce((a,b)=>a+b,0);
({cart, discounted, total});

Example 4 — forEach()

Perform action for each array element (no return value).

const fruits = ["apple","banana","cherry"];
let logs = "";
fruits.forEach((f,i)=> logs += `${i+1}. ${f}\n`);
logs;

Example 5 — Callback Demo

Passing greet to processUser and logging result.

function greetLog(name){ return `Hello, ${name}!`; }
function processUserReturn(name,callback){ return callback(name); }
processUserReturn('Ayush',greetLog);

Higher-Order Functions (HOFs)

What is a Higher-Order Function (HOF)?

Why Use Higher-Order Functions?

Example 1 — Function as Argument (Callback)

Example 2 — Function Returning Another Function

Example 3 — map(), filter(), reduce()

Example 4 — forEach()

Example 5 — Callback Demo