A $1.00 charge is a temporary preauthorization placed by your credit card company or PayPal. This charge is placed by your bank or PayPal in order to authorize your account, essentially giving Codecademy the green light to charge your card for the full amount if you decide to proceed with Pro once your trial is over in the coming 7 days.
The charge may stay pending for a few days, however, your bank or PayPal will eventually remove this charge.