CODEWITHSUNDEEP
javascriptasync.js
akronymn
akronymn

Reputation: 2446

async.filter is calling callback before all iterators finish

I am using caolan's async.js. I'm confused why the callback is getting called before all of the iterators are done. When I run the following code:

  async.filter(matched_objects.fields, function(item, callback) {
      console.log('checking field: ' + item.id);
      if(item.id == 130 || item.id == 131) {
        console.log('calling field true: ' + item.id);
        callback(true);
      } 
      callback(false);
    },
    function(fieldResults) {
      console.log('fieldsResults.length=' + fieldResults.length);
    });

I get the following output:

checking field: 130 
calling field true: 130 
fieldsResults.length=1 
checking field: 131
calling field true: 131

It doesn't make any sense to me that the console.log in the callback is getting called before the second results.fields item is checked in the filter loop.

Upvotes: 1

Views: 3975

Answers (2)

Mrchief
Mrchief

Reputation: 76228

The problem is the callback(false) is called everytime, even if you hit the if condition. The right approach would be to add a return statement:

if(item.id == 130 || item.id == 131) {
  console.log('calling field true: ' + item.id);
  return callback(true);  // now you won't call callback(false) everytime
} 
callback(false);

And you can even shorten the filter by saying:

callback(item.id == 130 || item.id == 131);

Upvotes: 6

akronymn
akronymn

Reputation: 2446

After more experimentation I've discovered the problem was the callback(false); line. apparently this caused the filter to exit. I guess this makes sense since it forces the callback to be called.

Upvotes: 0

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