Figuring the complexity of Promise.all

Question

I have been struggling for quite some time to get this multiple async nodejs request apis to work but unfortunately i am not able to get them work.

Index.js Code:

service.get(
  "/restraunts",
  versionRoutes({
    "1.0.0": getRestrauntsList
  })
);

function getRestrauntsList(req, res, next) {
  console.log("Started getRestrauntsList");
  file1
    .appEnvironment(req, res, next)
    .then(function(result) {
      return file2.getRestrauntsList(req, res, next);
    })
    .then(function(result) {
      res.status(200).send(result);
      return;
    })
    .catch(function(errorResult) {
      res.status(500).send(errorResult);
      return;
    });
}

File2.js

module.exports = {
  getRestrauntsList: function(req, res, next) {
    console.log("getRestrauntsList started..");
    var cities = [1, 2, 3, 4, 5];
    let restrauntsList = [];
    let urlArray = [];
    var restrauntsListPromise = cities.map(function(id) {
      return new Promise(function(resolve, reject) {
        var options = {
          method: "GET",
          url: "someurl/" + id + "/restaurants",
          headers: {
            "AUTH-TOKEN": "TOKEN"
          }
        };
        request(options, function(error, response, body) {
          if (error) {
            if ("message" in error) {
              errorMsg = error.message;
              var result = {
                status: "error",
                message: errorMsg
              };
            } else {
              var result = {
                status: "error",
                message: "Resource Timeout."
              };
            }
            reject(result);
            return promise;
          }
          console.log(
            "Response: " + JSON.stringify(response)
          );
          if (response.statusCode === 200 || response.statusCode === 201) {
            body = JSON.parse(body);
            if (body.success) {
              let result = {
                status: "success",
                data: body.result
              };
              resolve(result);
            } else {
              let result = {
                status: "error",
                message: body.error
              };
              reject(result);
            }
          } else {
            let result = {
              status: "error",
              message: body.error
            };
            reject(result);
          }
        });
      });
    });
    console.log('restrauntsListPromise:' + JSON.stringify(restrauntsListPromise));
    Promise.all(restrauntsListPromise).then(function(result) {
      var content = result.map(function(restraunts) {
        return restrauntsList.push(restraunts.body);
      });
      //  res.send(content);
      resolve({
        restrauntsList: restrauntsList
      });
      return promise;
    });
  },
};

Ideally i expect to get the response of all the apis in the

restrauntsListPromise

and then using Promise.all i should iterate all the promises and formulate my required object.

The response of my code however is

restrauntsListPromise:[{},{},{},{},{}]

and then

Response: {"statusCode":200,"body":"{\"success\":true,\"res

Response: {"statusCode":200,"body":"{\"success\":true,\"res

Response: {"statusCode":200,"body":"{\"success\":true,\"res

Response: {"statusCode":200,"body":"{\"success\":true,\"res

Response: {"statusCode":200,"body":"{\"success\":true,\"res

Ideally what should happen is i should be able to pass the combined result of all the five apis calls as a single object back to the calling promise here

.then(function(result) {
    res.status(200).send(result);
    return;
  })

The problem being the method getRestrauntsList finishes execution and then after some time, i get the responses of the apis.

return restrauntsList.push(restraunts.body); is wrong. You are returning the return value of push(). Is that what you want? — marekful
i would want to return the results of all the 5 apis calls as a single object and access that in .then(function(result) { res.status(200).send(result); return; }) — Doe
The code is hard to understand because of poor indentation. You could use request-promise for starters to get rid of that nested functions. — Estus Flask
"i should be able to pass the combined result " — If you want to combine them, then you need to write code to do that (in whatever way you want them combined). — Quentin

Sridhar Sridhar · Accepted Answer · 2018-07-24T06:27:38

The problem being the method getRestrauntsList finishes execution and then after some time, i get the responses of the apis.

This is because you're not returning a promise from the getRestrauntsList().

There are few items that needs to addressed to make it work

1. Remove the unused variables

return promise; // both inside promise.all[] and request()

There is no declared variable named promise. So, you can remove it.

2. Accessing .body instead of .data

You're resolving as resolve({status: "success", data: body.result}); But When you are iterating, you are accessing using .body instead of .data. You need to be using .data. Also, you can eliminate restrauntsList array since you're using a .map()

3. Calling resolve() to return values.

You can't use resolve() to return value within Promise.all[] since you didn't create a promise using new Promise((resolve, reject) => { ... });. By default, a return within a promise will be a promise. so, a simple return will suffice. But if you want to be explicit, you can also return using Promise.resolve()

Making those changes,

return Promise.all(restrauntsListPromise).then(function (result) {
  return {
    restrauntsList: result.map(function (restraunts) {
      return restraunts.data;
    })
  };

  //or using Promise.resolve();
  // return Promise.resolve({
  //   restrauntsList: result.map(function (restraunts) {
  //     return restraunts.data;
  //   })
  // });
});

Figuring the complexity of Promise.all

2 Answers