exports.index = function(req, res) {
moviedb.indexMovie()
 .then(x => {
    Movie.findAsync()
      .then(responseWithResult(res))
      .catch(handleError(res))
      }
  )
};

function responseWithResult(res, statusCode) {
   statusCode = statusCode || 200;
   console.log("Populating Response");
   return function(entity) {
    if (entity) {
      res.status(statusCode).json(entity);
    }
  };
}

The above code works perfectly fine, the returned function in the responsewithresult function, gets populated with the .then response. However, I was experimenting and tried this instead, but it did not work. Please explain why?

exports.index = function(req, res) {
  moviedb.indexMovie()
    .then(x => {
       Movie.findAsync()
        .then(x => {responseWithResult(res)}) // <-- this doesn't work
        .catch(handleError(res))
    })
};

exports.index = function(req, res) {
moviedb.indexMovie()
 .then(x => {
    Movie.findAsync()
      .then(responseWithResult(res))
      .catch(handleError(res))
      }
  )
};

function responseWithResult(res, statusCode) {
   statusCode = statusCode || 200;
   console.log("Populating Response");
   return function(entity) {
    if (entity) {
      res.status(statusCode).json(entity);
    }
  };
}

The above code works perfectly fine, the returned function in the responsewithresult function, gets populated with the .then response. However, I was experimenting and tried this instead, but it did not work. Please explain why?

exports.index = function(req, res) {
  moviedb.indexMovie()
    .then(x => {
       Movie.findAsync()
        .then(x => {responseWithResult(res)}) // <-- this doesn't work
        .catch(handleError(res))
    })
};

• javascript
• promise
• bluebird

2 Answers 2

It doesn't work since

.then(responseWithResult(res))

passes the result of responseWithResult (which is a function that eventually returns a value) to the then function, whereas

x => {responseWithResult(res)}

which is logically like

function(x) {
  responseWithResult(res);
}

and when you put that inside then(...), nothing is returned.

You could fix that with

then(x => responseWithResult(res))

which is like

function(x) {
  return responseWithResult(res);
}

but really you should refractor your entire function to make better use of promises, and have a cleaner code in the end:

exports.index = function(req, res) {
  moviedb.indexMovie()
   .then(() => Movie.findAsync())
   .then(movie => responseWithResult(movie, res))
   .catch(() => handleError(res))
};

function responseWithResult(entity, res, statusCode) {
  statusCode = statusCode || 200;
  console.log("Populating Response");
  res.status(statusCode).json(entity);
}

Because you're returning undefined, add a return before the responseWithRest call or remove the {}s around it to make it an expression arrow function.

Promises work by return value.

Your first example doesn't sequence operations either. The functions get invoked immediately.