How do i obtain the values from pending promises?

Question

Im currently having trouble getting the output below. Can somebody tell me what is wrong with the code that prevents me from getting the following output that i want? Thanks in advance!

Code:

 // http requests
 const getJSON = require('get-json');

 function getShopLocation(postalCode) {
 // Use promise to resolve when success
 return new Promise((resolve, reject) => {
 // One Map API is used to retrieve Lat & Lon & more map details
 var oneMapURL = `https://developers.onemap.sg/commonapi/search?searchVal=${postalCode}&returnGeom=Y&getAddrDetails=Y&pageNum=1`;
 getJSON(oneMapURL, function(error, response) {

 if (response) {
  // Get only the lat
  var lat = response.results[0].LATITUDE;
  // Resolve the location details
  resolve(lat);
} else {
  reject(error);
}
});
});
}

 function init() {
    var postalCode = [ 519498, 629117, 670445, 258748, 238884 ];
    var title = ['Place A', 'Place B', 'Place C', 'Place D', 'Place E'];
    var data = [];

    var i = 0;
    for (i = 0; i < postalCode.length; ++i) {
        var lat = getShopLocation(postalCode[i]);
        data.push({ title: title[i] , lat: lat});
    }

    Promise.all(data)
    .then((results) => {
        console.log("Data Output: ", results);
    })
    .catch((e) => {
        // Handle errors here
        console.log(error);
    });
    }
    init();

Output I want:

[
  { title: 'Place A', lat: 1.322595392 },
  { title: 'Place B', lat: 1.325617641 },
  { title: 'Place C', lat: 1.325617641 },
  { title: 'Place D', lat: 1.3835802030000002 },
  { title: 'Place E', lat: 1.3061957990000002 }
]

Bergi · Answer 1 · 2020-03-14T16:34:53.130

1

As you use data with Promise.all, it should be an array of promises. And getShopLocation returns a promise for the latitude, not the actual latitude.

You probably want to use

for (let i = 0; i < postalCode.length; ++i) {
    var latPromise = getShopLocation(postalCode[i]);
    var objPromise = latPromise.then(lat => ({ title: title[i] , lat: lat}));
    data.push(objPromise);
}

edited Mar 14 '20 at 16:34

answered Mar 14 '20 at 13:56

Bergi

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im getting an undefined value for the title. – scorezel789 Mar 14 '20 at 14:34
@scorezel789 [oops](https://stackoverflow.com/q/750486/1048572) – Bergi Mar 14 '20 at 16:35

Jasdeep Singh · Accepted Answer · 2020-03-14T14:08:37.307

You are pushing objects to data array which are not actally promises. You need to push actual promises to an array to use them inside Promise.all

I have made the required changes in your code to function properly, please use the below code:

 // http requests
 const getJSON = require('get-json');

 function getShopLocation(postalCode) {
   // Use promise to resolve when success
   return new Promise((resolve, reject) => {
     // One Map API is used to retrieve Lat & Lon & more map details
     var oneMapURL = `https://developers.onemap.sg/commonapi/search?searchVal=${postalCode}&returnGeom=Y&getAddrDetails=Y&pageNum=1`;
     getJSON(oneMapURL, function(error, response) {

       if (response) {
         // Get only the lat
         var lat = response.results[0].LATITUDE;
         // Resolve the location details
         resolve(lat);
       } else {
         reject(error);
       }
     });
   });
 }

 function init() {
   var postalCode = [519498, 629117, 670445, 258748, 238884];
   var title = ['Place A', 'Place B', 'Place C', 'Place D', 'Place E'];
   var data = [];

   var i = 0;
   var promiseArr = [];
   for (i = 0; i < postalCode.length; ++i) {
     var lat = getShopLocation(postalCode[i]);
     promiseArr.push(lat);
   }

   Promise.all(promiseArr)
     .then((results) => {
       console.log("Data Output: ", results);
       for (let j = 0; j < promiseArr.length; j++) {
         data.push({
           title: title[j],
           lat: promiseArr[j],
         })
       }
       console.log(data); // This is my final answer.
     })
     .catch((e) => {
       // Handle errors here
       console.log(error);
     });
 }
 init();

im getting an error: `ReferenceError: promisesArr is not defined`.. — scorezel789, Mar 14 '20 at 14:06
Apologies, spelling mistake from my side, i would request you to copy my code again for your code. — Jasdeep Singh, Mar 14 '20 at 14:09
Thanks for your help! I'm still a newbie in using promises. Im really greatful for your help (: Going to give you a thumbs up for this. So basically its just pushing the promise to Promise.all and iterate all over again to get both the objects. — scorezel789, Mar 14 '20 at 14:23

How do i obtain the values from pending promises?

2 Answers2