Chrome Apps are structured similarly to extensions so current developers will recognize the manifest and packaging methods. When you're done, you'll just need to produce a zip file of your code and assets in order to publish your app.
A Chrome App contains these components:
  • The manifest tells Chrome about your app, what it is, how to launch it and the extra permissions that it requires.
  • The background script is used to create the event page responsible for managing the app life cycle.
  • All code must be included in the Chrome App package. This includes HTML, JS, CSS and Native Client modules.
  • All icons and other assets must be included in the package as well.

First create your manifest.json file (Formats: Manifest Files describes this manifest in detail):
{
  "name": "Hello World!",
  "description": "My first Chrome App.",
  "version": "0.1",
  "manifest_version": 2,
  "app": {
    "background": {
      "scripts": ["background.js"]
    }
  },
  "icons": { "16": "calculator-16.png", "128": "calculator-128.png" }
}
Important: Chrome Apps must use manifest version 2.
Next create a new file called background.js with the following content:
chrome.app.runtime.onLaunched.addListener(function() {
  chrome.app.window.create('window.html', {
    'bounds': {
      'width': 400,
      'height': 500
    }
  });
});
In the above sample code, the onLaunched event will be fired when the user starts the app. It then immediately opens a window for the app of the specified width and height. Your background script may contain additional listeners, windows, post messages, and launch data, all of which are used by the event page to manage the app.
Create your window.html file:
Hello, world!
Copy these icons to your app folder:
Many of the Chrome Apps APIs are still experimental, so you should enable experimental APIs so that you can try them out:
  • Go to chrome://flags.
  • Find "Experimental Extension APIs", and click its "Enable" link.
  • Restart Chrome.
To load your app, bring up the apps and extensions management page by clicking the settings icon  and choosing Tools > Extensions.
Make sure the Developer mode checkbox has been selected.
Click the Load unpacked extension button, navigate to your app's folder and click OK.
Once you've loaded your app, open a New Tab page and click on your new app icon.
These command line options to Chrome may help you iterate:
  • --load-and-launch-app=/path/to/app/ installs the unpacked application from the given path, and launches it. If the application is already running it is reloaded with the updated content.
  • --app-id=ajjhbohkjpincjgiieeomimlgnll launches an app already loaded into Chrome. It does not restart any previously running app, but it does launch the new app with any updated content.

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