icon ajax loading

[eric cuver]

Hello everyone

I would like a advice what time you advise me to the start of a loading icon ajax when I put it the  ajax started  and the loading icon comes only after the ajax ends

from browser import document, ajax

def on_complete(req):
    if req.status==200:
        document["result"].html = req.text
    else:
        document["result"].html = "error "+req.text

icons load there ??? 
req.open('GET', url+'?'+qs, True)
req.set_header('content-type', 'application/x-www-form-urlencoded')
req.send()