Cannot find name 'keyof'

Question

i'm trying to use the keyof keyword in typescript but it seems to be not found. I'm using typescript 3.5.2 with angular 7.2.2 Thanks in advance.

export class Functions {

  static ListObjectProperties(): string[] {
        let array = keyof Foo;
        return array;
  }
}

I get "Cannot find name 'keyof'"

Answer 1

You can only use keyof in a type context. For instance:

interface Foo { aProperty: unknown }

const x: keyof Foo = "aProperty"