# Quick start
## Introduction
Generally, atom-shell enables you to create desktop applications with pure
JavaScript by providing a runtime with rich native APIs. You could see it as
a variant of the Node.js runtime which is focused on desktop applications
instead of web servers.
It doesn't mean atom-shell is a JavaScript binding to GUI libraries. Instead,
atom-shell uses web pages as its GUI, so you could also see it as a minimal Chromium
browser, controlled by JavaScript.
### The browser side
If you have experience with Node.js web applications, you will know that there
are two types of JavaScript scripts: the server side scripts and the client side
scripts. Server-side JavaScript is that which runs on the Node.js
runtime, while client-side JavaScript runs inside the user's browser.
In atom-shell we have similar concepts: Since atom-shell displays a GUI by showing
web pages, we have **scripts that run in the web page**, and also **scripts run by the atom-shell runtime**, which creates those web pages.
Like Node.js, we call them **client scripts**, and **browser scripts** (meaning the browser replaces the concept of the server here).
In traditional Node.js applications, communication between server and
client is usually facilitated via web sockets. In atom-shell, we have provided
the [ipc](../api/ipc-renderer.md) module for browser to client
communication, and the [remote](../api/remote.md) module for easy RPC
support.
### Web page and Node.js
Normal web pages are designed to not reach outside of the browser, which makes them
unsuitable for interacting with native systems. Atom-shell provides Node.js APIs
in web pages so you can access native resources from web pages, just like
[Node-Webkit](https://github.com/rogerwang/node-webkit).
But unlike Node-Webkit, you cannot do native GUI related operations in web
pages. Instead you need to do them on the browser side by sending messages to it, or
using the easy [remote](../api/remote.md) module.
## Write your first atom-shell app
Generally, an atom-shell app would be structured like this (see the [hello-atom](https://github.com/dougnukem/hello-atom) repo for reference):
```text
your-app/
├── package.json
├── main.js
└── index.html
```
The format of `package.json` is exactly the same as that of Node's modules, and the
script specified by the `main` field is the startup script of your app, which
will run on the browser side. An example of your `package.json` might look like
this:
```json
{
"name" : "your-app",
"version" : "0.1.0",
"main" : "main.js"
}
```
The `main.js` should create windows and handle system events, a typical
example being:
```javascript
var app = require('app'); // Module to control application life.
var BrowserWindow = require('browser-window'); // Module to create native browser window.
// Report crashes to our server.
require('crash-reporter').start();
// Keep a global reference of the window object, if you don't, the window will
// be closed automatically when the javascript object is GCed.
var mainWindow = null;
// Quit when all windows are closed.
app.on('window-all-closed', function() {
if (process.platform != 'darwin')
app.quit();
});
// This method will be called when atom-shell has done everything
// initialization and ready for creating browser windows.
app.on('ready', function() {
// Create the browser window.
mainWindow = new BrowserWindow({width: 800, height: 600});
// and load the index.html of the app.
mainWindow.loadUrl('file://' + __dirname + '/index.html');
// Emitted when the window is closed.
mainWindow.on('closed', function() {
// Dereference the window object, usually you would store windows
// in an array if your app supports multi windows, this is the time
// when you should delete the corresponding element.
mainWindow = null;
});
});
```
Finally the `index.html` is the web page you want to show:
```html
<!DOCTYPE html>
<html>
<head>
<title>Hello World!</title>
</head>
<body>
<h1>Hello World!</h1>
We are using node.js <script>document.write(process.version)</script>
and atom-shell <script>document.write(process.versions['atom-shell'])</script>.
</body>
</html>
```
## Run your app
After you're done writing your app, you can create a distribution by
following the [Application distribution](./application-distribution.md) guide
and then execute the packaged app.
You can also just use the downloaded atom-shell binary to execute your app directly.
On Windows:
```cmd
$ .\atom-shell\atom.exe your-app\
```
On Linux:
```bash
$ ./atom-shell/atom your-app/
```
On Mac OS X:
```bash
$ ./Atom.app/Contents/MacOS/Atom your-app/
```
`Atom.app` here is part of the atom-shell's release package, you can download it from [here](https://github.com/atom/atom-shell/releases).