Summary - Arrow functions

Write a list filtering program with arrow functions.

Summary - Arrow functions

Arrow functions provide concise syntax, lexical this, and use as a type. Together they enable clean and safe code in filtering, mapping, and callback-based operations.

let sayilar = [1, 2, 3, 4, 5];
let buyukler = sayilar.filter((n: number) => n > 3);
// buyukler: [4, 5]

Arrow functions make functional programming patterns easy in TypeScript.

Exercise List filtering program

Declare an array named sayilar with value [1, 2, 3, 4, 5]. Use the .filter() method with an arrow function to filter numbers greater than 3. Print the first element of the filtered array with console.log.

Show example solution

let sayilar = [1, 2, 3, 4, 5];
let buyukler = sayilar.filter((n: number) => n > 3);
console.log(buyukler[0]);

Test yourself

Why is an arrow function preferred in a callback inside a method?
- Because it preserves the enclosing method's this
- Because it is faster
- Because it can take more parameters
- Because it prevents errors
Show answer

Because it preserves the enclosing method's this — An arrow function takes <code>this</code> lexically; in a callback inside a method, <code>this</code> is not lost. In a regular function, <code>this</code> changes by call site and is lost.

Add the filter threshold value

let sayilar = [1, 2, 3, 4, 5];
let buyukler = sayilar.filter((n: number) => n > ____);

Show answer

let sayilar = [1, 2, 3, 4, 5];
let buyukler = sayilar.filter((n: number) => n > 2);

Arrow functions summary

(a, b) => a + b

Short function syntax
Arrow this

From lexical scope
(x: number) => number

Function type
Arrow callback

Use in filtering and mapping

Next lesson: What is an interface?

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