How to get the value of the first promise that succeeds in the promises chain

Question

I am looking for a way to return a promise only if another promise fails .

How can i do this?

promises that I look like this (of course, I delete the unrelated code):

getUserByUsername = function(username) {
    return promise(function(resolve, reject) {
       user = userModel.getByUsername(username);
       if ( user ) { resolve(user); } else { reject("user not found"); }
    });
};

getUserByEmail = function(email) {
    return promise(function(resolve, reject) {
       user = userModel.getByEmail(email);
       if ( user ) { resolve(user); } else { reject("user not found"); }
    });
};

checkPassword = function(user, password) {
    return promise(function(resolve, reject) {
       if ( user.isValidPassword(password) ) { resolve() } else { reject("password mismatch"); }
    });
};

And I want to combine them in the following sequence

• Call getUserByUsername, then reject, then callgetUserByEmail
• Returns a whoever value that resolves from the two promises above OR, if both promises reject the entire chain.
• Call checkPasswordwith value and, if he rejects, reject the whole chain

So far I have done this and it seems to work. (I use when.js btw)

getUserByUsername(usernameOrEmail)
.then( 
    function(user) { return user; }, 
    function() { return getUserByEmail(usernameOrEmail) } 
)
.then( function(user) { return checkPassword(user, password) } )
.done( 
    function() { console.log('success'); }, 
    function(err) { console.log('failure', err) }
);

, , , ( , ).

Answer 1

- :

 getUserByUsername(usernameOrEmail).
 catch(getUserByEmail.bind(null, usernameOrEmail)).
 then(function(user){
     if(!isValidPassword(user, password)) throw new Error("Invalid Password");
 }).then(function(){
     // success
 }, function(){
    //fail
 });

:

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