From Learn About the Ext JavaScript Library

Question 1: After I submit a form to server-side. How can I easy know server-side throw out an error or not.

The main reason I ask this is that I want to handle next step.

If everything ok, I want to move to next page. If something wrong, I want to keep in currently page.

form_acc.submit({
	waitMsg:'Creating new account now...'
});	
 
// need catch server-side information, if error, keep currently dialog 
// if success, make currently dialog disappear
 
// if (successFlag)  --- ? how to define this flag
    aAddAccDlg.hide();

This tutorial is incorrect and performs a lot of extra and unnecessary work. Form's understand JSON data natively. You do not need to configure a store. You can simply set a reader on the form config and then call form.load({options}) -- this is where you specify the url, method(post,get), etc.