Typescript: How to Ensure Tuple Type is Explicit and Not Combined

I have a code snippet that defines a person object and a function to get its values:

const person = {
  name: "abc",
  age: 123,
  isHere: true
};

const getPersonValues = () => {
  return [person.name, person.age, person.isHere];
};

const [name] = getPersonValues(); // type for "name" is string | number | boolean

In the above code, the type for name is shown as string | number | boolean, but I want it to be strictly a string. Is there a way to achieve this without explicitly declaring the exact type inside getPersonValues?

Answer №1

To give an array a tuple type, you can utilize the as const syntax. This not only enforces the type to be readonly, but if it's solely used for destructuring the return value, then there's no issue.

const fetchUserData = () => {
  return [user.name, user.age, user.isActive] as const;
};

Playground Link

Answer №2

Unfortunately, that won't work.

When TypeScript examines the array, it identifies multiple possible types and defines it as

Array<string | number | boolean>
.

To resolve this issue, you must provide more specific type information.

const getPersonValues = () => {
    return [person.name, person.age, person.isHere] as [string, number, boolean];
};

Answer №3

If we consider another option, we could refactor the code to return an object like this:

const user = {
  username: "xyz",
  age: 25,
  isActive: true
};

const getUserInfo = () => {
  return user;
};

const {username, isActive} = getUserInfo(); // username is of type 'string', isActive is of type 'boolean'

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