A Strong Mode for JavaScript(docs.google.com)

    interface BreadIngredientOptions {
      flourType?: String; // this is the syntax for optional strings
      sugarAmount?: String; // ditto: it's the ? that makes it optional
      // ...
    }

    function bakeBread(ingredientOverrides: BreadIngredientOptions) {
      // ...
    }

    // callers don't need to explicitly inherit or implement to be type checked
    // however, since all properties are optional, this is less interesting
    bakeBread({
      flourType: 'white'
    });

    interface MyArgumentInterface {
      requiredArg: number;
      optionalArg?: number;
    }

    function f(args: MyArgumentInterface) {
      // ...
    }

    // This works:
    f({
      requiredArg: 10,
      optionalArg: 5
    });

    // This also works:
    f({ requiredArg: 50 });

    // This statically throws at compile time:
    f({ optionalArg: 10 });