What is the best way to pass resolved promise values down to a final "then" chain [duplicate]

Question

I'm trying to get my head around promises, using the Q module in node.js, however I have a small issue.

In this example:

ModelA.create(/* params */) .then(function(modelA){     return ModelB.create(/* params */); }) .then(function(modelB){     return ModelC.create(/* params */); }) .then(function(modelC){      // need to do stuff with modelA, modelB and modelC  }) .fail(/*do failure stuff*/); 

The .create method returns a promise then in each .then(), as expected one gets the resolved value of the promise.

However in the final .then() I need to have all 3 previously resolved promise values.

What would be the best way to do this?

Answer 1

These are some of your many options:

Behind door 1, use reduce to accumulate the results in series.

var models = []; [     function () {         return ModelA.create(/*...*/);     },     function () {         return ModelB.create(/*...*/);     },     function () {         return ModelC.create(/*...*/);     } ].reduce(function (ready, makeModel) {     return ready.then(function () {         return makeModel().then(function (model) {             models.push(model);         });     }); }, Q()) .catch(function (error) {     // handle errors }); 

Behind door 2, pack the accumulated models into an array, and unpack with spread.

Q.try(function () {     return ModelA.create(/* params */) }) .then(function(modelA){     return [modelA, ModelB.create(/* params */)]; }) .spread(function(modelA, modelB){     return [modelA, modelB, ModelC.create(/* params */)]; }) .spread(function(modelA, modelB, modelC){     // need to do stuff with modelA, modelB and modelC }) .catch(/*do failure stuff*/); 

Behind door 3, capture the results in the parent scope:

var models []; ModelA.create(/* params */) .then(function(modelA){     models.push(modelA);     return ModelB.create(/* params */); }) .then(function(modelB){     models.push(modelB);     return ModelC.create(/* params */); }) .then(function(modelC){     models.push(modelC);      // need to do stuff with models  }) .catch(function (error) {     // handle error });