Keep a collection of completed promises stored in the inventory

Question

Keep a collection of completed promises stored in the inventory

Good day,

I'm facing a challenge in Parse Javascript where I am trying to save items after receiving them in a loop. However, outside the loop, the array of objects remains empty.

.. define global ** var filesUpload = []**

 for (var key in files) {
         var photoUpload = new Parse.File(String(file.name),[file.image])
             photoUpload.save().then(function(item) {
                    deferred.resolve(item)

                    filesUpload.push(deferred.promise)


             }, function(error) {
                console.log("error to save file"+JSON.stringify(error))
                // The file either could not be read, or could not be saved to Parse.
            })
         }

--> end of loop

filesUpload array still has no items

javascript parse-platform promise

Answer 1

Answer №1

If you want to retrieve values from multiple promises, you will need to utilize the Promise.all method. While Parse.com does not have a direct implementation of Promise.all, they offer a similar alternative:

Parse.Promise.when(files.map(function(file){
    return new Parse.File(String(file.name),[file.image]).save();
})).then(function(){
    var results = Array.prototype.slice.call(arguments);
    //results === your filesUpload
}).then(null, function(err){
    console.log("error to save file" + JSON.stringify(error));
});

If you prefer using Promise.all:

Promise.all(files.map(function(file){
    return new Parse.File(String(file.name),[file.image]).save();
})).then(function(results){
    //results === your filesUpload
}).catch(function(err){
    console.log("error to save file" + JSON.stringify(error));
});

In addition, I included the Promise.prototype.catch which may not be available in the Parse.Promise implementation. However, most promises do support this method. For instance, ES6 Promises offer both Promise.all and Promise.prototype.catch methods.

Answer 2

If you want to retrieve values from multiple promises, you will need to utilize the Promise.all method. While Parse.com does not have a direct implementation of Promise.all, they offer a similar alternative:

Parse.Promise.when(files.map(function(file){
    return new Parse.File(String(file.name),[file.image]).save();
})).then(function(){
    var results = Array.prototype.slice.call(arguments);
    //results === your filesUpload
}).then(null, function(err){
    console.log("error to save file" + JSON.stringify(error));
});

If you prefer using Promise.all:

Promise.all(files.map(function(file){
    return new Parse.File(String(file.name),[file.image]).save();
})).then(function(results){
    //results === your filesUpload
}).catch(function(err){
    console.log("error to save file" + JSON.stringify(error));
});

In addition, I included the Promise.prototype.catch which may not be available in the Parse.Promise implementation. However, most promises do support this method. For instance, ES6 Promises offer both Promise.all and Promise.prototype.catch methods.

Answer 3

Answer №2

Asynchronous promises add an extra layer of complexity to your code. When dealing with promises, keep in mind that any code following your for loop will execute before the promise is resolved and the then function is called.

It's like trying to do this:

window.setTimeout(function() {
  document.write('inside setTimeout');
}, 1000);

document.write('after call to setTimeout');

Make sure to handle any operations involving filesUpload within the then callback of your photoUpload.save() promise. It's a good practice to extract a function and call it from there for better organization.

 for (var key in files) {
   var photoUpload = new Parse.File(String(file.name), [file.image]);
   photoUpload.save().then(function(item) {
     deferred.resolve(item);

     filesUpload.push(deferred.promise);
     goAhead();

   }, function(error) {
     console.log("error to save file" + JSON.stringify(error));
       // The file either could not be read, or could not be saved to Parse.
   });
 }

 function goAhead() {
   // go ahead
 }

Answer 4

Asynchronous promises add an extra layer of complexity to your code. When dealing with promises, keep in mind that any code following your for loop will execute before the promise is resolved and the then function is called.

It's like trying to do this:

window.setTimeout(function() {
  document.write('inside setTimeout');
}, 1000);

document.write('after call to setTimeout');

Make sure to handle any operations involving filesUpload within the then callback of your photoUpload.save() promise. It's a good practice to extract a function and call it from there for better organization.

 for (var key in files) {
   var photoUpload = new Parse.File(String(file.name), [file.image]);
   photoUpload.save().then(function(item) {
     deferred.resolve(item);

     filesUpload.push(deferred.promise);
     goAhead();

   }, function(error) {
     console.log("error to save file" + JSON.stringify(error));
       // The file either could not be read, or could not be saved to Parse.
   });
 }

 function goAhead() {
   // go ahead
 }

Keep a collection of completed promises stored in the inventory

Answer №1

Answer №2

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