Asynchronous Javascript Callback functions

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Hello,

I have an issue in to write javascript asynchronous functions with ajax, my problem is that I have written 3 function with return boolean.

JavaScript

function getname(a,b)
{
.. $ajax here 
 {
    success(data)
       {
         if (data.resultvalue == true){
            return true;
         }
         else
         {
            return false;
         }
      }
   }
}
=============================================================
function validate(a)
{
.. $ajax here 
  {
     success(data)
        {
          if (data.resultvalue == true){
             return true;
          }
          else
          {
             return false;
          }
       }
  }
}
=============================================================
function checken(a)
{
.. $ajax here 
  {
     success(data)
        {
          if (data.resultvalue == true){
             return true;
          }
          else
          {
             return false;
          }
       }
  }
}
=============================================================
function callallfunctions()
{
   var aval = document.getelementbyid('myval');
   if (getname(aval.value,'abc') == true)
   {
      if (validate('abc') == true)
      {
         if (checken('def') == true)
         {
            return true
         }
         else
         {
            return false;
         }
      }
      else
      {
         return false;
      }
   }
   else
   {
      return false;
   }
}

Its working asynchronously and return value false while ajax is under processing. When i merge all the functions in one function then its working asynchronously too and return value false while ajax is under processing

Posted 13-Feb-15 3:30am

adeez

Updated 13-Feb-15 4:03am

Wendelius

v3

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Comments

ZurdoDev 13-Feb-15 9:50am

What is your question?

Since it runs asynchronously you can't return a value because the function ends before your ajax calls finishes. You need to re-write your code so that in success something happens instead of trying to return a value.

2 solutions

Solution 1

Sorry, but, to start with, it looks like you are clueless about basics of programming, not only extremely flexible JavaScript programming. Look:

C#

if (checken('def') == true)
{
   return true
}
else
{
   return false;
}

This is the same as

JavaScript

return chechen('def') // I have no idea what is "chechen"

Isn't that obvious? And so on…

So, first, you have to get such basics things and write code in humane manner. This is not really hard to do. Only then we can discuss something else.

—SA

Posted 13-Feb-15 5:24am

Sergey Alexandrovich Kryukov

Comments

Richard Deeming 13-Feb-15 12:16pm

Not precisely true in javascript. If checken('def') returns something that isn't a boolean, the longer version converts it to a boolean depending on its "truthiness", whereas the shorter version returns it unchanged.

The equivalent one-liner would be:
return !!checken('def');

Sergey Alexandrovich Kryukov 13-Feb-15 12:29pm

Oh, good point and the pattern. Agree.

Just a note: as the intent was to return true or false object, the intent for the use of the return value could be using it in another "if". And the ultimate "if" will eliminate this difference. So, in practice, the ultimate result will be the same. Agree?

I think the JavaScript development philosophy is rather ignoring the difference between different objects null, undefined, 0, false and other objects behaving identically under "if". In other words, even though if (something === null) or if (something === true) (the opposite, most strict check) can be used to detect the difference between undefined, true, null or any other objects, consistent use of if (something) will still give consistent results. This is a matter of individual approach, but the "if" techniques should be consistent.

Thank you for this important note.

—SA

adeez 13-Feb-15 15:51pm

thank you Sergey Alexandrovich Kryukov and all members for fast response :)
actually upper define functions are just for examples

return chechen('def') // I have no idea what is "chechen"

checken is function name I used it just for example and I know I can't do it without any callback function but may be I am clueless about basics of javascript programming :)

Sergey Alexandrovich Kryukov 13-Feb-15 16:11pm

All right, fix your code appropriately...
—SA

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Richard Deeming · Accepted Answer · 2015-02-13T07:08:00

As Ryan said, you can't return a value directly, because the function returns before the asynchronous AJAX method has completed.

You need to re-write your code to use a more asynchronous approach. For example:

JavaScript

function getname(a, b)
{
    return $.ajax(...);
}

function validate(a)
{
    return $.ajax(...);
}

function checken(a)
{
    return $.ajax(...);
}

function callallfunctions()
{
    var aval = document.getelementbyid('myval');

    return getname(aval.value, 'abc')
        .then(function(getnameResult){ return !!getnameResult.resultvalue ? validate('abc') : false; })
        .then(function(validateResult){ return !!validateResult.resultvalue ? checken('def') : false; })
        .then(function(checkenResult){ return !!checkenResult.resultvalue });
}

This uses jQuery's implementation of JavaScript Promises[^] to chain the asynchronous calls together.

Your calling code can then use the .done()[^] and .fail()[^] methods to register functions which will be called when all three methods have been completed, or when one of the methods fails.

JavaScript

callallfunctions()
    .done(function(result){ alert(result); })
    .fail(function(){ alert("Failed"); });

Asynchronous Javascript Callback functions

2 solutions

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Solution 1

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