Getting Started

Meta Engineer?

Unless you are specifically working on open source Hack code, you want Facebook's internal documentation instead for dev environment setup. If you're just looking to learn the Hack language itself, skip this Getting Started section.

1. Installation

The HHVM package includes everything you need to work with Hack, including the runtime and typechecker.

See the HHVM installation page to find the package relevant for your platform.

2. Initialize A Project

Create a directory with a .hhconfig file in it. This will be the root of your project.

$ mkdir my_project
$ cd my_project
$ touch .hhconfig

3. Write Your First Hack Program

Create a file called my_project/hello.hack with the following code:

use namespace HH\Lib\IO;

async function main(): Awaitable<void> {
  await IO\request_output()->writeAllAsync("Hello World!\n");

4. Run The Typechecker

Normally you'll get type errors and hover information from within your IDE. You can also run the typechecker directly to confirm that you have no type errors in any files in your project.

$ cd my_project
$ hh_client
No errors!

5. Run Your Program

HHVM provides the Hack runtime. You can run your program as follows:

$ cd my_project
$ hhvm hello.hack
Hello World!

6. Run A Website

Normally you'll start HHVM as a webserver, and it will automatically pick up any changes to files you make.

$ cd my_project
$ hhvm -m server -p 8080

You can now visit http://localhost:8080/hello.hack to see "Hello World!" in your browser.

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