Alfresco - Different javascript ?

I'm trying to create a new page in Alfresco, but the tutorials gives to me the information that i have to create three files: new-page.get.js new-page.html.ftl and new-page.get.xml , like Aikau - http://ift.tt/1LIAJSt

But when I'm trying to programming the javascript, "alert is not defined, window is not defined" and I see in the tutorials that I have to made models and widgets. I can't programming the javascript like a normal javascript ? Where I access more information about this javascript ? I can't programming this.