here's how a promise chain that has multiple input (including recursive input) looks

q.js

function authenticate(input) {
    if(isNumber(input)) {
       return getUsernameById(input)
       .then(function (username) {
         return getUser(username);
       })
       // chained because we will not need the user name in the next event
       .then(function (user) {
         return getPassword()
         // nested because we need both user and password next
         .then(function (password) {
            if (user.passwordHash !== hash(password)) {
                throw new Error("Can't authenticate");
            }
         });
      });
    } else if(isString(input)) {
       return getUsernameByEmail(input)
       .then(function (username) {
         return getUser(username);
       })
       // chained because we will not need the user name in the next event
       .then(function (user) {
         return getPassword()
         // nested because we need both user and password next
         .then(function (password) {
            if (user.passwordHash !== hash(password)) {
                throw new Error("Can't authenticate");
            }
         });
      });
    } else if(isObject(input)) {
       return Account.find().where(input).exec()
       .then(function (username) {
         return getUser(username);
       })
       // chained because we will not need the user name in the next event
       .then(function (user) {
         return getPassword()
         // nested because we need both user and password next
         .then(function (password) {
            if (user.passwordHash !== hash(password)) {
                throw new Error("Can't authenticate");
            }
         });
      });
    } else if(isArray(input)) {
       // lolwut
    }
}