This page is not a part of the application app1, it is a simple HTML page, or the page of another application.
Here you cannot use the function GoTo() because it is undefined, e.g. if you try this link: GoTo('page1.html') you will get a javascript error.
You can go to the page of the application from which you came here only by pressing the button back in the browser. If you try to link to it like this: page2.html , it will not work, because the page will be openned in the browser as a simple html page (like this one) not as a page of the application app1. Try to click it and see that the transitions in 'page2.html' will not work. View the source of page2.html and notice that additional code added by the framework is missing (the logo is missing too).