Requires the URL calls to be intercepted from the WebView. See https://gist.github.com/mrkev/4602188

Obj-C + JS communication - JS Side

App = new Object();
// Send message to application
// with the format osx:selector:attr1:attr2:etc...
App.sel = function (sel){
    var iframe = document.createElement('iframe');
    iframe.setAttribute('src', 'osx:' + sel);
    document.documentElement.appendChild(iframe);
    iframe.parentNode.removeChild(iframe);
    iframe = null;
}