How do I define an array of keys of an object in TypeScript?

Example:

const obj = {
  red: 0,
  blue: 1
};

// Doesn't work
const test: keyof obj[] = ['red', 'blue'];

CodePudding user response：

You have two problems.

First, you are referring to a value obj as a type, which is not allowed. You can get the type of a value with the typeof keyword.

Second, keyof Something[] will get you keyof (Something[]), the keys of the array type, and not (keyof Something)[], which is what you want here. You can use parentheses to fix that.

Putting that together looks like:

const obj = {
  red: 0,
  blue: 1
};

const test: (keyof typeof obj)[] = ['red', 'blue'];

See playground

Although most often you'd want to declare a type for obj on it's own, so it's easier to use and reference elsewhere.

interface MyType {
  red: number
  blue: number
}

const obj: MyType = {
  red: 0,
  blue: 1
};

const test: (keyof MyType)[] = ['red', 'blue'];

See playground

CodePudding user response：

One solution is:

const test: Array<keyof typeof obj> = ['red', 'blue'];