greeter-fn.ts

interface Person {
    firstName: string;
    lastName: string;
}

function greeter(person: Person): string {
    return "Hello, " + person.firstName + " " + person.lastName;
}

// Jasmine spec:
describe("greeter", function() {
    it("returns greeting", function() {
        expect(
            greeter({firstName: 'James', lastName: 'Hetfield'})
        ).toEqual('Hello, James Hetfield');
    });
});