Google Chrome App - check if app or regular site

I am working on project which will run as Chrome App & regular site.

How can I test/check in my JS if I am in an Chrome App? (i.e. some functionality will only work under chrome)

Just FYI, here is my Chrome App manifest, please note I am running this in the developer mode (directly from the source, not packaged yet)

{
    "manifest_version": 2,
    "name": "Example KIOSK APP",
    "version": "1.1",
    "icons": {
        "16": "images/icon-16.png",
        "48": "images/icon-48.png",
        "128": "images/icon-128.png"
    },
    "app": {
        "background": {
            "scripts": ["background.js"],
            "persistent": true
        }
    },
    "kiosk_enabled": true,
    "offline_enabled": true,
    "permissions": [
        "system.display",
        "power",
        "webview",
        "fileSystem",
        "alwaysOnTopWindows",
        "system.storage",
         "<all_urls>"
    ]
}

Any suggestions much appreciated.

Turns out the question meant to distinguish between identical code running in a webpage and inside a (regular) Chrome App window.

It is enough to test for Chrome App APIs that are never exposed to regular pages. An example of that would be to test for app.runtime:

if (window.chrome && chrome.app && chrome.app.runtime) {
  // Running inside a Chrome App context
} else {
  // Either not Chrome, or not as an app window
}