Typed Arrays
Declare arrays where every element must be the same type.
Syntax
let nums: number[] = [1, 2, 3];An array type describes a list whose elements all share a type. There are two equivalent ways to write it:
number[]— an array of numbers.Array<number>— the generic form, same meaning.
If you try to push a value of the wrong type, TypeScript reports an error.
Example
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When to use it
- A product list component declares its items as Product[] so TypeScript prevents accidentally mixing in non-product objects.
- A function returns string[] from a database query so callers can safely call string methods on every element.
- An analytics module stores number[] for page view counts, allowing typed reduce and map operations.
More examples
Declare a typed array
Shows three typed array declarations and demonstrates that push rejects an element of the wrong type.
const names: string[] = ['Alice', 'Bob', 'Carol'];
const scores: number[] = [98, 72, 85];
const flags: boolean[] = [true, false, true];
names.push(42); // Error: Argument of type 'number' is not assignableGeneric Array<T> syntax
Uses the generic Array<T> syntax as an alternative to T[], and defines a generic helper to retrieve the first element.
const ids: Array<number> = [1, 2, 3];
const tags: Array<string> = ['ts', 'web', 'types'];
function first<T>(arr: Array<T>): T | undefined {
return arr[0];
}Typed array from map
Declares an array of interface objects and infers the correct string[] type from a map call over it.
interface Product {
id: number;
name: string;
price: number;
}
const products: Product[] = [
{ id: 1, name: 'Pen', price: 1.99 },
{ id: 2, name: 'Notebook', price: 4.49 },
];
const names: string[] = products.map((p) => p.name);
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