Typescript build issues when importing a TS interface (and using `outFile`)

[billyvg]

I'm running into a TS issue:

Cannot compile modules using option 'outFile' unless the '--module' flag is 'amd' or 'system'.ts(6131)

I'm trying to import a TS interface e.g.

// foo.ts
export interface Foo {}

// index.ts
import {Foo} from './foo';