Node.js Promise.all() hanging

Question

Node.js Promise.all() hanging

Kind of stuck on this one. Working with https://github.com/then/promise on node.js

exports.count = function ( models, callback ) {
  var promises = [];

  models.forEach(function ( name ) {
    promises.push( countOne( name ) );
  });

  Promise.all( promises ).then(function ( res ) {
    callback( null, res );
  });

  Promise.resolve(promises[0]).then(function (res) {
    console.log('resolved individual with res', res);
  });
};

function countOne ( exampleArg ) {
  return new Promise(function ( resolve, reject ) {
    // It resolves or rejects
  });
}

I've also tried:

Promise.all( promises.map(function ( it ) { return Promise.resolve(it); }) ).then(function ( res ) {
  callback( null, res );
});

Either way, Promise.all doesn't fire the then. Promise.resolve does, however, give the appropriate response.

javascript
node.js
promise

Answer 1

ether one of your promises isn't resolving, in which case, your need to find out which one.

I think you are trying to do that with that console.log. if you do that with a forEach you can attach a log message to all promises and see which one isn't resolving / rejecting.

Or one of the promises is rejecting, which you are not handling.

I took the liberty of rewriting your code, try it like this:

exports.count = function (models, callback) {
    var allCounts = models.map(countOne);

    // second parameter is the onRejected handler
    Promise.all(allCounts).then(function (res) {
        callback(null, res);
    }, function (err) {
        callback(err);
    });

    promises[0].then(function (res) {
        console.log('resolved individual with res', res);
    });
};

I left in the callback, but I really would just return the promise, much simpler, much cleaner.

ProTip™:
Switch to the bluebird promise library, and replace your implementation with one line:

exports.count = function (models, callback) {
    Promise.map(models, countOne).nodeify(callback);
}

It will probably be faster to.