Another way to do it could be to store the value of k on the request
object (also untested):
var req = new qx.io.request.Xhr("/hrm/services/ActionServlet2", "POST");
req.setUserData("reqid", k);
req.addListener("success", function(e) {
var req = e.getTarget();
console.log(req.getUserData("reqid");
}, this);
On 17.05.2013 17:18, Derrell Lipman wrote:
> On Fri, May 17, 2013 at 11:04 AM, fei wang <wang...@romeo-foxtrot.com
> <mailto:wang...@romeo-foxtrot.com>> wrote:
>
> Hi,
>
> the follow is my snipplet code:
>
> //----------------------------------------------------------------
> __arr : ['A', 'B', 'C', 'D', 'E', 'F'],
>
> fillData : function() {
> for(var k=0; k<this.arr.length; k++) {
> var args = ...
> var req = new qx.io.request.Xhr("/hrm/services/ActionServlet2", "POST");
> req.setRequestData({
> 'class' : 'InternalDAO',
> 'method' : 'queryCommentAndScore',
> 'async' : false,
> 'args' : args
> });
> req.addListener("success", function(e) {
> console.log("k=" + k); // Here, the value
> is always '6', why?
> // BUT, My intention is to print 0, 1, 2,
> 3, 4, 5. How shoud I do?
> }, this);
>
> req.send();
> }
> }
>
> Your loop quickly sends out six requests, adds a listener function which
> will be called when the Xhr response is returned, and then returns to
> the browser. The final value of k, before returning to the browser and
> before any instance of your listener function was called, is 6. The
> "closures" that allow each of the listener functions to access that
> now-out-of-scope variable, k, therefore each have that final value of k
> before it went out of scope: 6.
>
> This is a very common problem encountered by people new to JavaScript.
> There are various ways to solve the problem. JavaScript does not provide
> block-level scope, so there is no pretty way to do it. Here's one
> solution (untested):
>
> function getNewListener(index)
> {
> return function(e)
> {
> console.log("k=" + index);
> };
> }
>
> req.addListener("success", getNewListener(k), this);
>
>
> Here, the getNewListener() function is called with each value of k, and
> so each call instance has an index parameter which is used in the
> returned function. Since each index parameter is unique, the closure has
> a unique value to print in console.log.
>
> Read up on closures. It's a key aspect of JavaScript, and very
> confusing, initially.
>
> Cheers,
>
> Derrell
>
>
>
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security visibility with the essential security capabilities. Easily and
efficiently configure, manage, and operate all of your security controls
from a single console and one unified framework. Download a free trial.
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