Currently, I'm using Array.apply(null, new Array(10)).map(Number.prototype.valueOf, 0); to create an array of 0.
I'm wondering is there a better (cleaner) way to do this in typescript?
4 Answers
Update! This is now supported out of the box (see TypeScript Playground).
You no longer need to extend the Array interface.
Old answer:
You can add to the open Array<T> interface to make the fill method available. There is a polyfill for Array.prototype.fill on MDN if you want older browser support.
interface Array<T> {
fill(value: T): Array<T>;
}
var arr = Array<number>(10).fill(0);
Eventually the fill method will find its way into the lib.d.ts file and you can delete your one (the compiler will warn you when you need to do this).
Comments
As of now you can just do
const a = new Array<number>(1000).fill(0);
Make sure you include <number> otherwise it will infer a's type as any[].
4 Comments
michael
This is driving me crazy. It fails in the latest typescript compiler.
% tsc --version Version 3.9.2 % cat ./fill.ts const a = new Array<number>(1000).fill(0); % tsc ./fill.ts fill.ts:1:35 - error TS2339: Property 'fill' does not exist on type 'number[]'. 1 const a = new Array<number>(1000).fill(0);
Timmmm
You probably need to change the
target setting in tsconfig.json.michael
That's right. Array.fill is ES6, so target must specify ES6. Thank you for the tip!
Robo Robok
I don't like this approach, because Array<number>(1000) is invalid assumption and it's easy to cause a bug if you change the fill, for example, or split creation and filling to separate variables.
You could pass an integer argument to the Array constructor, this will return a new JavaScript array with its length property set to that number, plus you can use .fill to fill all the elements of an array from index zero.
const data = Array(10).fill(0)
console.log(data)
Comments
Having reviewed the concept of array holes I would do:
Array.apply(null, new Array(10)).map(()=> 0);
Not a big saving but is some.
Array(10).fill(0).Int32Array(10)if it’s about numbers only.