Day 3: Arrays and Tuples

Managing Lists of Data

Welcome to Day 3! We’ve covered the basic primitives. Now let’s talk about collections. Most apps aren’t just single numbers or strings; they are lists of things.

Arrays

In TypeScript, there are two main ways to define an array.

Syntax 1: type[]

This is the most common syntax.

let numbers: number[] = [1, 2, 3, 4, 5];
let names: string[] = ["Alice", "Bob", "Charlie"];

Syntax 2: Array<type>

This uses the generic syntax (we’ll cover Generics deeply later).

let scores: Array<number> = [95, 82, 76];

Avoid any[]: Try not to use any[] (mixed arrays) unless absolutely necessary. It defeats the purpose of TypeScript.

Tuples

What if you need an array with a fixed number of elements, where each element has a specific type? That’s a Tuple.

Imagine representing a user record with an ID (number) and a Name (string).

// Define a tuple
let user: [number, string];

// Initialize it
user = [1, "Jack"]; // OK

// user = ["Jack", 1]; // Error: Type 'string' is not assignable to type 'number'.

Tuples are great for returning multiple values from a function or working with CSV-like data rows.

let rgb: [number, number, number] = [255, 0, 0];

Readonly Tuples

You can make tuples immutable (unchangeable).

let point: readonly [number, number] = [10, 20];
// point[0] = 5; // Error!

Challenge for Today

1. Create a file day3.ts.
2. Define an array of your favorite hobbies (strings).
3. Define a tuple that represents a “Person”: [name (string), age (number), isStudent (boolean)].
4. Try to add a fourth element to your tuple and see what happens (concept: fixed length).
5. Log the person’s name from the tuple.

See you on Day 4!