Summary - Arrays

Write a notes app by combining array types and methods.

Summary - Arrays

In this section you learned to specify array types as number[] and Array<number>, use the push, pop and map methods, define immutable arrays with readonly, and create nested arrays like number[][]. Now you will build a notes app combining all of these.

let notlar: readonly number[][] = [
    [80, 90],
    [70, 85]
];
// notlar.push([100]); // Error: readonly

Exercise Notes app

Define an array named notlar of type readonly number[][]: first row [80, 90], second row [70, 85]. Then use map to compute the sum of each row's two grades, store them in a number[] array called toplamlar, and print it.

Show example solution

let notlar: readonly number[][] = [
    [80, 90],
    [70, 85]
];
let toplamlar: number[] = notlar.map(satir => satir[0] + satir[1]);
console.log(toplamlar);

Test yourself

Which is a valid TypeScript array type notation?
- number{}
- string()
- number[]
- Array
Show answer

number[] — `number[]` and `Array<number>` are valid array type notations in TypeScript; curly braces or parentheses forms are invalid.

Define a readonly string array

let sabit: ____ = ["pzt", "sal"];

Show answer

let sabit: readonly string[] = ["pzt", "sal"];

Array concepts summary

number[]

Mutable number array
readonly number[]

Immutable number array
number[][]

Nested number array
Array<string>

Alternative notation for a string array

Next lesson: What is a tuple?

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