How to add controls in javascript mobile view?

I've created a mobile project and created a view then when i'm trying to add a control in the view i cannot do something like this

var myButton = new sap.m.Button("myButton", {text:"my button")};

and one more thing if i need to create an application that will work on both mobile and desktop must i create two separate projects one for the mobile and one for the desktop or is there is a way to use the same project for both

thanks in advance