detect ipad/iphone webview via javascript

This uses a combination of window.navigator.userAgent and window.navigator.standalone. It can distinguish between all four states relating to an iOS web app: safari (browser), standalone (fullscreen), uiwebview, and not iOS.

Demo: http://jsfiddle.net/ThinkingStiff/6qrbn/

var standalone = window.navigator.standalone,
    userAgent = window.navigator.userAgent.toLowerCase(),
    safari = /safari/.test( userAgent ),
    ios = /iphone|ipod|ipad/.test( userAgent );

if( ios ) {
    if ( !standalone && safari ) {
        //browser
    } else if ( standalone && !safari ) {
        //standalone
    } else if ( !standalone && !safari ) {
        //uiwebview
    };
} else {
    //not iOS
};

User Agents

Running in UIWebView

Mozilla/5.0 (iPad; CPU OS 5_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Mobile/98176

Running in Safari on iPad

Mozilla/5.0 (iPad; CPU OS 5_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9B176 Safari/7534.48.3

Running in Safari on Mac OS X

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3) AppleWebKit/534.55.3 (KHTML, like Gecko) Version/5.1.5 Safari/534.55.3

Running in Chrome on Mac OS X

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.151 Safari/535.19

Running in FireFox on Mac OS X

Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:11.0) Gecko/20100101 Firefox/11.0

Detection Code

var is_uiwebview = /(iPhone|iPod|iPad).*AppleWebKit(?!.*Safari)/i.test(navigator.userAgent);
var is_safari_or_uiwebview = /(iPhone|iPod|iPad).*AppleWebKit/i.test(navigator.userAgent);