Readonly Arrays

Readonly arrays make list inputs safer by preventing functions from mutating them.

readonly.ts

function firstTwo(values: readonly number[]): number[] {
    return values.slice(0, 2);
}

const extraValue: number = ;
const numbers: number[] = [3, 6, extraValue];
const preview: number[] = firstTwo(numbers);
const sum: number = preview[0] + preview[1];

console.log(`preview=${preview.join(",")}`);
console.log(`sum=${sum}`);

function firstTwo(values: readonly number[]): number[] {
    return values.slice(0, 2);
}

const extraValue: number = ;
const numbers: number[] = [3, 6, extraValue];
const preview: number[] = firstTwo(numbers);
const sum: number = preview[0] + preview[1];

console.log(`preview=${preview.join(",")}`);
console.log(`sum=${sum}`);

function firstTwo(values: readonly number[]): number[] {
    return values.slice(0, 2);
}

const extraValue: number = ;
const numbers: number[] = [3, 6, extraValue];
const preview: number[] = firstTwo(numbers);
const sum: number = preview[0] + preview[1];

console.log(`preview=${preview.join(",")}`);
console.log(`sum=${sum}`);

readonly array `readonly number[]` describes an array that code can read but should not modify.