Typescript interface problem: how to get the type like t when we have a const like list

Question

const list = [
  {
    label: "phone",
    defaultValue: "1203981209",
  },
  {
    label: "isMan",
    defaultValue: false,
  },
  {
    label: "age",
    defaultValue: 22,
  },
];

type t = {
  phone: string;
  isMan: boolean;
  age: number;
};

We have list.And how to get t in Typescript. I tried to write something like type t = {[k in typeof list[number]["label"]]: typeof list[number]["defaultValue"];};,but that does not work.

Answer 1

The original object needs to be typed well for this to work - since you want the literal label values for the keys in the new object, they need to be as const so they don't get widened to string. (I don't see a nice way to use as const over the whole object, because then the values don't get widened - if you went that route, you'd have to have a helper type to turn, eg, "1203981209" into string and so on).

const l = [
  {
    label: "phone" as const,
    defaultValue: "1203981209",
  },
  {
    label: "isMan" as const,
    defaultValue: false,
  },
  {
    label: "age" as const,
    defaultValue: 22,
  },
];
type T = {
    [Prop in typeof l[number] as Prop["label"]]: Prop["defaultValue"];
};