How is This Done?

var is_chrome = /chrome/.test( navigator.userAgent.toLowerCase() );
var is_safari = /safari/.test( navigator.userAgent.toLowerCase() );
var myvar = 0;
var myexit = 0;

if(is_chrome == true || is_safari == true) {
    YUI().use('history', function (Y) {
        var history = new Y.History({
            initialState: {kittens: null,}
          });
          
          history.addValue('kittens');
          
          Y.on('history:change', function (e) {
          if (myvar == 1){
              myexit=1;
              window.location ='/PAGEURL';
              }
          myvar=myvar + 1;
          });    
});
}
else{
YUI().use('history', function (Y) {
        var history = new Y.History({
            initialState: {kittens: 'cat',}
          });
          
          Y.on('history:change', function (e) {
              myexit=1;
              window.location ='/PAGEURL';
          });    
});
}