Closures and Higher-Order Functions

Closures and Higher-Order Functions

In this lesson — part of Advanced Features — you'll learn closures and higher-order functions in JavaScript and why it matters in real work.

Why it matters

Functions that take or return functions unlock concise, composable code.

Key ideas

• Functions as values
• map / filter / reduce
• Callbacks
• Composition

In practice

Here's how it looks in idiomatic JavaScript:

const nums = [1, 2, 3, 4, 5, 6];
const result = nums
  .filter(n => n % 2 === 0) // [2, 4, 6]
  .map(n => n * n);         // [4, 16, 36]
console.log(result);

JavaScript note: map and filter are higher-order array methods that take a callback and return a new array, so they chain cleanly without mutating the original.

Try it yourself

Exercise: In JavaScript, use map and filter to get the squares of the even numbers.

Recap

You now understand closures and higher-order functions and can apply it in JavaScript. Mark this lesson complete and continue to the next one.