Pass an anonymous new array to constructor

Issue

I'm writing some TypeScript code where I want to add an element to my Map. My Map is of type <number, number[]>, so when I add a new key-value pair I want to initialize the value to a new empty array.

I know that I can do this:

let arr: number[] = [];
myMap.set(i, arr);

But I would prefer to do this:

myMap.set(i, new number[]);

That is how it's done in C# and I was hoping I could do the same in TypeScript, but I'm having trouble finding how to do it. Perhaps I just have the wrong syntax?

Solution

If your Map is already typed (eg Map<number, number[]>), you don't need to type the arguments.

For a Map<K, V>, the signature for Map.prototype.set() is

(method) Map<K, V>.set(key: K, value: V): Map<K, V>

You can simply pass an empty array which will implicitly satisfy the number[] argument type

const myMap: Map<number, number[]> = new Map();
myMap.set(1, []);

TypeScript Playground

Answered By - Phil