greeter-fn-runtime-checked.js

function greeter(person) {
    if (!person || !person.firstName || !person.lastName) {
        throw new Error('invalid arguments');
    }

    return "Hello, " + person.firstName + " " + person.lastName;
}

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

    it("throws on invalid input", function() {
        expect(() => greeter()).toThrowError('invalid arguments');
        expect(() => greeter(5)).toThrowError('invalid arguments');
        expect(() => greeter({firstName: 'Jason'})).toThrowError('invalid arguments');
    });
});