How do you add polyfills to Globals in typescript (modules)

Question

I was able to find a polyfill(on stack overflow) for Array#includes and add it to typescript but after adding a small import to my file it turned into a module(I understand

Answer 1

You need to declare it in the global namespace:

declare global {
  interface Array {
      includes(searchElement: T) : boolean;
  }
}

More

Extending lib.d.ts is covered here : https://basarat.gitbooks.io/typescript/content/docs/types/lib.d.ts.html