How to declare a Fixed length Array in TypeScript

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The JavaScript array has a constructor that accepts the length of the array:

let arr = new Array<number>(3);
console.log(arr); // [undefined × 3]

However, this is just the initial size, there’s no restriction on changing that:

arr.push(5);
console.log(arr); // [undefined × 3, 5]

TypeScript has tuple types which let you define an array with a specific length and types:

let arr: [number, number, number];

arr = [1, 2, 3]; // ok
arr = [1, 2]; // Type '[number, number]' is not assignable to type '[number, number, number]'
arr = [1, 2, "3"]; // Type '[number, number, string]' is not assignable to type '[number, number, number]'

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