Redirect a wordpress widget after successful form submission

I have made a contact form widget for wordpress using their widget api it works but I want to send the user to a thank you page. The problem is the head开发者_如何学Pythoners have already been sent by the time the widget is processed. From what I understand I have to hook onto one of wordpresses actions to load the widget at the right time but I'm not sure how to do that.

I've seen this post Wordpress Widget Redirect Page and tried several things but I'm not having any luck.

You could use javascript to redirect the users page.