How To (elegantly) Interrupt Promises Chain Execution With Q

I have a chain of promises that looks like this: module.exports.deleteCommunityFollower = function deleteCommunityFollower(req, res){ var communityId = req.params.userId; var f

Solution 1:

Since you are using modern node, here is how I would write it using Q.async:

const deleteFollower = Q.async(function*(communityId, followerId){ 
    const community = new user_model.User(communityId);
    let followers = yield community.getFollower(followerId);
    if(followers.length) === 0; returnfalse;
    yield community.removeFollower(follower[0]);
    returntrue;
});

Reads like a synchronous function and completely flat, nice huh?

I omitted the code extracting things from req/res since that would make the code harder to test and it should probably be separated anyway. I'd call it like:

functionhandler(req, res){
    var communityId = req.params.userId;
    var followerId = req.session.passport.user.userId;
    deleteFollower(communityId, followerId).then(val => {
        if(val) res.sendStatus(201);
        else res.sendStatus(404);
    }).fail(err => {
        res.sendStatus(500);
        errorHelper.diagnosticsUploader(err); 
    });
}

(Note, personally I much prefer using the bluebird library for performance reasons, where I'd use Promise.coroutine).