Initialize object' properties from array - inline

Question

Here is my array:

const a = ['one', 'two'] as const;

Here is my object type:

type T = {
    { [key in typeof a[number]]: number;
}

Expected result:

const r: T = {
    one: 0,
    two: 0
}

This doesn't work:

const z: T = a.map((prop) => [prop, 0]);

It returns: Type '(number | "one" | "two")[][]' is missing the following properties from type 'T': one, two(2739)

map returns an array, not an object. You should pass the result of that map to Object.fromEntries(). — Heretic Monkey
– Heretic Monkey, Commented Jul 9, 2021 at 17:56

byte-this · Accepted Answer · 2021-07-09 17:58:01Z

1

Everything looks good until that last part. That last part should be:

const z: T = a.reduce((obj, prop) => ({...obj, [prop]: 0}), {} as T);

We are reducing the 'a' array to an object, starting it out as an empty object of type T (since we know it will be populated at the end of the reduction), then the callback adds each property and sets it to 0.

answered Jul 9, 2021 at 17:58

byte-this

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