Object type doesn't inherit all native obj methods

I create a type for a custom object shape like this:

type A = {
  readonly prop1: string;
  readonly prop2: string;
}

Then in a method I’m using it like so:

const getStuff = (obj: A) =>
   obj.reduce((acc, curr) => {
     ...
   })
}

It’s complaining that property 'reduce' does not exist on type A. I assumed A as an object type would inherit all the native methods of a JS object, but I guess not.

How can a I tell it to do that?

>Solution :

Because native javascript object doesn’t have a reduce method. Try obj.toString() or obj.hasOwnProperty(). Maybe you wanted to Array.reduce? If so, do it like this:

type A<T>  =  {
    readonly prop1: string;
    readonly prop2: string;
} & Array<T>;