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 TypeScript 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 TypeScript:

const nums = [1, 2, 3, 4, 5];
const evensDoubled = nums
  .filter((n) => n % 2 === 0)
  .map((n) => n * 2);
console.log(evensDoubled); // [4, 8]

TypeScript note: map and filter return new arrays and infer the result element type from the callback, leaving the original array untouched.

Try it yourself

Exercise: In TypeScript, 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 TypeScript. Mark this lesson complete and continue to the next one.