Default value for typescript type alias

Question

Can typescript type alias support default arguments? For instance:

export type SomeType = {
    typename: string;
    strength: number;
    radius: number;
    some_func: Function;
    some_other_stat: number = 8; // <-- This doesn't work
}

The error is A type literal property cannot have an initializer.

I can't find documentation relating to this - type keyword is very obscure behind everything else that is also named type. Is there anything I can do to have default argument value for type in typescript?

Answer 1

You cannot add default values directly to a type declaration.

You can do something like this instead:

// Declare the type
export type SomeType = {
    typename: string;
    strength: number;
    radius: number;
    some_func: Function;
    some_other_stat: number;
}

// Create an object with all the necessary defaults
const defaultSomeType = {
    some_other_stat: 8
}

// Inject default values into your variable using spread operator.
const someTypeVariable: SomeType = {
  ...defaultSomeType,
  typename: 'name',
  strength: 5,
  radius: 2,
  some_func: () => {}
}

Answer 2

Type does not exist in runtime, so a default value makes no sense. If you want to have a default default, you must use something that exists in runtime, such as a class or a factory function