Switch web site to mobile css client side with JQuery

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I am trying to change the display of my web pages depending on the version of the browser and space on screen. I need to completely change the look of the pages as follow:

• If the site is displayed on a mobile phone I want the mini version.
• If the site is displayed on a desktop browser but the size of the window is too small I want the mini version.
• If the site is displayed on a desktop browser and the window can accommodate the full version I want the full version displayed.
• If no javascript is available the full version should display.

I just started with some pretty basic code which relies on userAgent:\[code\]if( /Android|webOS|iPhone|iPad|iPod|BlackBerry/i.test(navigator.userAgent) )\[/code\]Is there a clean way to achieve what I'm trying to do with JQuery for example?