Summary - Arrays
- TypeScript course
- Beginner
- Lesson 15/89
- 4 min
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: readonlyPractice 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.
Starter code
// readonly iç içe not dizisi tanımla, her satırın toplamını map ile hesapla ve yazdırSample solution
let notlar: readonly number[][] = [
[80, 90],
[70, 85]
];
let toplamlar: number[] = notlar.map(satir => satir[0] + satir[1]);
console.log(toplamlar);Expected output
[ 170, 155 ]
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which is a valid TypeScript array type notation?
- number{}
- string()
- number[] Correct answer
- Array
Explanation: `number[]` and `Array<number>` are valid array type notations in TypeScript; curly braces or parentheses forms are invalid.
2 Define a readonly string array
let sabit: ____ = ["pzt", "sal"];let sabit: readonly string[] = ["pzt", "sal"];Explanation: `readonly string[]` defines an immutable string array; `string[]` or `Array<string>` does not add readonly protection.
3 Array concepts summary
| Term | Meaning |
|---|---|
number[] |
Mutable number array |
readonly number[] |
Immutable number array |
number[][] |
Nested number array |
Array<string> |
Alternative notation for a string array |