How to UPDATE a query with different arguments in MySQL

Environment

Node.js, MySQL (using node-mysql library connect)

At first

I could have one argument 'aaa' or two arguments 'aaa' and 'bbb'.

UPDATE user SET email = 'aaa' WHERE uid = 'xxx';
UPDATE user SET email = 'aaa', password = 'bbb' WHERE uid = 'xxx';

My problem

How could I use one query to overcome above cases? Like below ...

var sql = "UPDATE user SET email = ?, password = ? WHERE uid = ?;"
dbclient.query(sql, [email, password, uid], function (err, results) {
    ...
});

1. 
   

   If two arguments were defined, variable sql was :

   
   

   
   sql = "UPDATE user SET email = 'test@mail.com', password = 'abcd' WHERE uid = 1;";
   
   



2. 
   

   If someone argument was undefined, variable sql was :

   
   

   
   sql = "UPDATE user SET email = 'test@mail.com', password = password WHERE uid = 1;";