Promises in foreach

Question

I have a couple of code about some logic.

My following code block working as expected so willbeUpdated variable couldn't updated literally in syncronized way.

var willbeUpdated = 1;
anArray.forEach(function(i){
   getPromisedData(i).then(function(d){
       willbeUpdated += d;
   });

});
if (wiillbeUpdated == something) {
  // some logic
}

So question is that, Do I have to create again another promised method for that foreach logic and put outside if logic its then method, will be a best practise, or any other preferable idea in this situation ?

Edit: I asked this question to hear best or better approaches about nested async function handling instead of exact code blocks, thanks.

score 2 · Answer 1 · answered Dec 11 '15 at 21:33

2

Use Promise.all().

var willbeUpdated = 1,
    promises = [];
anArray.forEach(function(i){
   promises.push(getPromisedData(i));
});
Promise.all(promises).then(function() {
  // some logic
});

answered Dec 11 '15 at 21:33

Michał Perłakowski

88,409
26
156
177

score 1 · Answer 2 · answered Dec 11 '15 at 21:17

1

I think what you're looking for is to put the if block (willBeUpdated == something) inside the function that the getPromisedData resolves with.

So:

var willbeUpdated = 1;
anArray.forEach(function(i){
   getPromisedData(i).then(function(d){
       willbeUpdated += d;
       if (wiillbeUpdated == something) {
         // some logic
       }
   });

});

Would work out. If you can give me a better idea of what you're trying to do then there may be a better solution.

answered Dec 11 '15 at 21:17

Richard

1,138
1
6
11

In the case of simple incrementation, it could work, but will not wait for all the tasks to end and will do something before finished with the tasks. – dsdenes Dec 11 '15 at 21:28
In this way , if logic will run as array length count. – İlker Korkut Dec 11 '15 at 21:30

score 1 · Answer 3 · answered Dec 11 '15 at 21:22

1

q and many other promise libraries can handle promise arrays, and wait for their result.

var q = require('q');
var willbeUpdated = 1;
var todo = [];

anArray.forEach(function(i){
  todo.push(getPromisedData(i).then(function(d) {
    return (willbeUpdated+= d);
  }));
});

q(todo).then(function() {
  if (wiillbeUpdated == something) {
    // some logic
  }      
});

answered Dec 11 '15 at 21:22

dsdenes

1,025
6
15

Your and @Gothdo's answers seems ok, but the problem is not code exactly, for instance, in nested loops It will be ugly pushing promises return values to get its latest value, is this solution the only way? – İlker Korkut Dec 11 '15 at 22:30

Promises in foreach

3 Answers3