Return result from asynchronous callback function

Question

I have seen lots of posts on stackoverflow regarding getting the returned value of an asynchronous call in a callback function but I would like to know if I could get the result without going much inside the callback.

For Eg: Current Scenario:

myFunc(arg1,arg2, mycallback);
..
function mycallback(values)
{
//Process values
alert(values);
}

What I would like to have:

var returnedValues = myFunc(arg1,arg2, function mycallback(values)
{
return values;
});

// Now I would to use the returnedValues here...

Is the above scenario possible? Kindly let me know.

Cheers.

All the posts you saw probably gave the same answer that this can not be done. — , Jun 28 '15 at 00:28

score 0 · Answer 1 · answered Jun 28 '15 at 00:11

You cannot do that, what you could do is make use of Promises

Quote: ...I could get the result without going much inside the callback.

If you are concerned about the callback hell, that is something you can mitigate by using promises:

Example from bluebird library:

You should use promises to turn this:

fs.readFile("file.json", function(err, val) {
    if( err ) {
        console.error("unable to read file");
    }
    else {
        try {
            val = JSON.parse(val);
            console.log(val.success);
        }
        catch( e ) {
            console.error("invalid json in file");
        }
    }
});

Into this:

    fs.readFileAsync("file.json").then(JSON.parse).then(function(val) {
        console.log(val.success);
    })
    .catch(SyntaxError, function(e) {
        console.error("invalid json in file");
    })
    .catch(function(e) {
        console.error("unable to read file")
    });

score 0 · Answer 2 · answered Jun 28 '15 at 00:12

You can use a promise library. Here is implementation using jQuery promise

(function ($) {
    function myFunc(arg1,arg2){
          var defer = $.Deferred(),
              result=arg1+arg2; 
          defer.resolve(result);
          return defer.promise();
    }

    myFunc(1,2).then(function(result){
        console.log('result is: '+result)
        //manipulate result as you want
        result=result+1;
        showFinalResult(result);
    });
    function showFinalResult(result){
        alert(result);
    }
})(jQuery);

http://jsfiddle.net/gfmvgc8p/

Return result from asynchronous callback function

2 Answers2