Registration Flow (promises)

registration_flow_ promises.js

let pwd, email, user;
UserFlow.validateEmail(email)
   .then(UserFlow.checkUserExists) // Check if user exists
   .then(function(existingUser){ // Spitting custom exception
     if( existingUser ){
       throw Error('User exists')
     }
   }).then(() => {
     return UserFlow.hashPassword(pwd); // Hash password
   }).then((hashedPwd)=>{
      return UserFlow.createUser(email, hashedPwd); // Actually creating user in the databse
   }).then((newUser) => {
     user = newUser // Saving user to later reference
     return sendEmail(user, pwd) // Sending an email to the user
   }).then(() => {
     return user // Returning the user object (model)
   });