How can I view nodes on my site from Drupalgap?
In mymodule_sample_page() just return an empty div container, for example:

&lt;div id="my_node_11"&gt;&lt;/div&gt;

Then attach a pageshow handler to your page via hook_menu(), then in the pageshow handler call node_load(), and in its success inject the content into your empty div container.

The page_callback can not have any async calls in it, as all async calls have to be handled after the page is actually shown.

FYI, DrupalGap has built in support to view nodes, just navigate to node/11 in the app. Here's a brief example demonstrating pageshow: http://www.drupalgap.org/node/154