If your target is ES5 you will have to provide polyfills. Typescript will unfortunately typecheck even if you don't have polyfills and you'll get runtime errors

If your target is ES5 you will have to provide polyfills. Typescript will unfortunately typecheck even if you don't have polyfills and you'll get runtime errors with your ES5 target. They specifically said they won't provide polyfills and they Will continue to typecheck even if your target does not support the standard function.