Username to be same as email address ( create User Wizard)

Hello there
I have a create user wizard.  and i have change the text next to the username to email so user will enter an email address
for the user name. So i want the email field to be the same but not have the user type it out twice,  Within the wizard how
would make the email field auto populate same as the username once the user name has been filled out.?
 
Regards
Rob
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