Hello World

Hello World

Tutorial Exercise


“Hello, World!” will get you writing some TypeScript and familiarize yourself with the Exercism workflow. Completing it unlocks the rest of the TypeScript Track.

Watch our "Introduction to Hello, World" video to get started 👇


The classical introductory exercise. Just say "Hello, World!".

"Hello, World!" is the traditional first program for beginning programming in a new language or environment.

The objectives are simple:

  • Modify the provided code so that it produces the string "Hello, World!".
  • Run the test suite and make sure that it succeeds.
  • Submit your solution and check it at the website.

If everything goes well, you will be ready to fetch your first real exercise.


Go through the setup instructions for TypeScript to install the necessary dependencies:



Install assignment dependencies:

$ yarn install

Making the test suite pass

Execute the tests with:

$ yarn test

In many test suites all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by changing xit to it.


This section is a step-by-step guide to solving this exercise.

This exercise has two files:

  • hello-world.ts
  • hello-world.test.ts

The first file is where you will write your code. The second is where the tests are defined.

The tests will check whether your code is doing the right thing. You don't need to be able to write a test suite from scratch, but it helps to understand what a test looks like, and what it is doing.

Open up the test file, hello-world.test.ts. There is a single test inside:

it('says hello world', () => {
  expect(hello()).toEqual('Hello, World!')

Run the test now, with the following command on the command-line:

$ yarn test

The test fails, which makes sense since you've not written any code yet.

The failure looks like this:

    × says hello world (5ms)

  ● Hello World › says hello world

    expect(received).toEqual(expected) // deep equality

    Expected: "Hello, World!"
    Received: "Goodbye, Mars!"

      4 |
      5 |   it('says hello world', () => {
    > 6 |     expect(hello()).toEqual('Hello, World!')
        |                     ^
      7 |   })
      8 |
      9 | })

      at Object.it (hello-world.test.ts:6:32)

And these are those code lines with probable defects in the hello-world.test.ts file:

the 6th line:

    expect(hello()).toEqual('Hello, World!')

Hence the problem is with the hello() function call. We can see that the test is expecting 'Hello, World!' as output, but instead is getting "Goodbye, Mars!".

So let's check now this function in the hello-worlds.ts file:

export function hello(): string {
  return 'Goodbye, Mars!'

Now we see that the function returns the incorrect string, which is the reason for our failure. Let's fix this by changing the returned value:

export function hello(): string {
  return 'Hello, World!'

Run the test again:

 PASS  ./hello-world.test.ts
  Hello World
    √ says hello world (4ms)

And it passes!

Edit via GitHub The link opens in a new window or tab
TypeScript Exercism

Ready to start Hello World?

Sign up to Exercism to learn and master TypeScript with 97 exercises, and real human mentoring, all for free.