是否可以在没有用户提交表单的情况下保存表单数据？

I am trying to create a signup/login form. I want to have a single form field. As the user types their email address into the field, the email address is checked against the user database. If the email is found in the user database a password field is displayed, and the user logs in after entering their password. I am trying to create a signup/login form. I wa