Calling functions asynchronous

Question

I want to initiate a Database request, which takes several time and responses with an Integer (42). The setTimeout in dbRequest() is representative for this request.

The responded integer should be incremented by 1 in the function initRequest. Therefore initRequest should return 43.

var dbRequest = function () {

  setTimeout(function(){
    console.log('Hello World! => 42');
    return 42;
  }, 5000);

};

var initRequest = function (cb){
  var test = cb() + 1;
  console.log('Incremented Value: ' + test);
  return test;
};

initRequest(dbRequest);

Unfortunately var test = cb() + 1; is not waiting for the setTimeout and calculates with NaN. The output:

Incremented Value: NaN
// 5 sec delay
Hello World! => 42

How can I make this function asynchronous, so that initRequest waits for dbRequest response?

You seem to have things backwards. The function _is_ asynchronous, that means that it doesn't wait. — Barmar, Apr 19 '14 at 14:18
Anything that depends on the result of an asynchronous action has to be done in its callback function. Javascript is single-threaded, it can't stay in the original function and also execute the asynchronous call at the same time. — Barmar, Apr 19 '14 at 14:19
Basically the same issue has here: http://stackoverflow.com/questions/14220321/how-to-return-the-response-from-an-ajax-call That question deals with `AJAX` requests instead of `setTimeout`, but it's the same asynchronous issue — cookie monster, Apr 19 '14 at 14:23
why dont you call the function after 5 seconds on which you will passed 42, and do some action(increment) with this? — Suman Bogati, Apr 19 '14 at 14:24

Suman Bogati · Answer 1 · 2014-04-19T16:04:35.237

Exactly don't know about your case but to get the desire result you could do something like this.

var dbRequest = function (callback) {
    setTimeout(function(){
        console.log('Hello World! => 42');
        callback(42);
    }, 5000);
};

function initRequest(val){
    var test = val + 1;
    console.log('Incremented Value: ' + test);
}

 dbRequest(initRequest);

Call the callback function after particular time, and pass the value with this invoked function for desire action.

Calling functions asynchronous

1 Answers1