update Javascript Global Variable

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I am working in asp.net development, I have Two files i.e.
i) UserControl
ii).js (javascript)

In .js File following is code

JavaScript

var varBindNewSalesTranGrid = '';
function BindNewSalesAttribute() {
   $.ajax({
      type: "POST",
      url: "/url of Webmthod returns string",
      data: '{}',
      contentType: "application/json; charset=utf-8",
      dataType: "json",
      success: function (data) {
          varBindNewSalesTranGrid += data.d;
      },
      error: function (xhr, ajaxOptions, thrownError) {
      }
   });
}

In Usercontrol file

JavaScript

$(document).ready(function () {
    BindNewSalesAttribute();
    alert(varBindNewSalesTranGrid);
});
//Which is file referenced above .js file

When I run my usercontrol file I see the value of varBindNewSalesTranGrid is empty ('').Function returns value 'TestString' and I am assigning value varBindNewSalesTranGrid in BindNewSalesAttribute function but still value is not getting updated.
if you have any ideas then let me know.

Posted 13-Oct-14 4:43am

RAHUL(10217975)

Updated 13-Oct-14 5:11am

Sergey Alexandrovich Kryukov

v2

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Sergey Alexandrovich Kryukov 13-Oct-14 11:33am

I formatted the code samples in your post. Please click Improve question to see how it should be done, do it properly next time.
—SA

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Sergey Alexandrovich Kryukov · Answer 1 · 2014-10-13T05:32:00

This is just the sequence of asynchronous operations. You don't update your variable in your function BindNewSalesAttribute; you do it in the function success. When your function BindNewSalesAttribute returns, the function object success is created, but not yet called, so the variable varBindNewSalesTranGrid is not yet updated. It will be updated when HTTP request is sent to the server side, the server side process it and sends HTTP response, which is handled on your client side by calling the function success of your $.ajax object.

To check it up, just call your alert in your success function, but also do some visually noticeable in your error function, in case the HTTP request is unsuccessful.

By the way, here you can observe the effect of closure. Please see:
http://en.wikipedia.org/wiki/Closure_%28computer_programming%29[^],
http://en.wikipedia.org/wiki/JavaScript#Functional[^].

What to do? Redesign your code to avoid using an assumption of the order of calls of the functions in question. Avoid using outer-scope variables, which are best avoided. You need to abstract out your success/error actions from your library function BindNewSalesAttribute. Say, you can do it by adding a couple of function parameters (along with some other parameters).

—SA