Open webpage in fullscreen in Safari on iOS

No, there is no way to toggle the fullscreen mode in Safari on iOS using javascript.

In order for a web page to run in fullscreen mode, you need to add the following meta tag, and the page needs to be started from a bookmark on the home screen:

<meta name="apple-mobile-web-app-capable" content="yes">

However, you can detect if the page is running in fullscreen mode or not with javascript using the read only property:

window.navigator.standalone