[Javascript] XMLHttpRequest()

[Terry Riegel]

Second post, I'll try not to be annoying, but maybe if I ask a little  
differently.

I have this little snip of code...

    xhr.open('post', url, false);
    xhr.setRequestHeader('Content-Type','application/x-www-form- 
urlencoded');
    xhr.onreadystatechange = function() { self.onComplete(); };
    xhr.send(parameters);

The 'false' in the open request waits until the open returns as  
opposed to if I said 'true' it would work asynchronously. How would I  
make it 'true' and then when it did return do the rest of the code in  
the snip? (Similar to a onSuccess or onFailure trigger) I hope this  
makes sense.

Any help will be appreciated.


Terry Riegel





On Nov 15, 2007, at 5:52 PM, Terry Riegel wrote:

> Hello everyone. Things have been quiet for a while. I am trying to  
> get some of my existing code compatible with Safari 3, and have  
> found a little snag that maybe an expert would see a quick solution  
> to.
>
> I have a PeriodicalAjax function (listed below in its entirety) and  
> it worked great on all the browsers I had tested it with until  
> Safari 3 came out. I discovered the line
>
> xhr.open('post', url, true);
>
> was not working properly and code never seemed to execute beyond  
> it. So I looked it up and the third parameter basically tells JS to  
> make the open a blocking open or a non-blocking open. Apparently  
> with it set to true the code would execute the open request and  
> continue  with or without a response. So to fix things I changed it  
> to...
>
> xhr.open('post', url, false);
>
> This did make it so the function and web page now works as it  
> should, but since the code is stopping and waiting for the open  
> everything seems sluggish and the browser become so slow it is  
> unusable.
>
> What I would like to do is make the subsequent code execute only  
> when the open is successful. Is there an easy way to try the open  
> then sleep for 10ms and then try again??
>
> Any help will be greatly appreciated.
>
>
> Thanks,
>
>
> Terry Riegel
>
>
>
>
> function PeriodicalAjax(url, parameters, frequency, decay,  
> onSuccess, onFailure) {
>  function createRequestObject() {
>   var xhr;
>   try {
>    xhr = new XMLHttpRequest();
>   }
>   catch (e) {
>    xhr = new ActiveXObject("Microsoft.XMLHTTP");
>   }
>   return xhr;
>  }	
>  function send() {
>   if(!stopped) {
>    xhr.open('post', url, false);
>    xhr.setRequestHeader('Content-Type','application/x-www-form- 
> urlencoded');
>    xhr.onreadystatechange = function() { self.onComplete(); };
>    xhr.send(parameters);
>   }
>  }
>  this.stop = function() {
>   stopped = true;
>   clearTimeout(this.timer);
>  }
>  this.start = function() {
>   stopped = false;
>   this.onTimerEvent();
>  }	
>  this.onComplete = function() {
>   if(this.stopped) return false;
>   if ( xhr.readyState == 4) {
>    if(xhr.status == 200) {
>     if(xhr.responseText == lastResponse) {
>      decay = decay * originalDecay;
>     } else {
>      decay = 1;
>     }
>     lastResponse = xhr.responseText;
>     if(onSuccess instanceof Function) {
>      onSuccess(xhr);
>     }
>     this.timer = setTimeout(function() { self.onTimerEvent(); },  
> decay * frequency * 1000);
>    } else {
>     if(onFailure instanceof Function) {
>      onFailure(xhr);
>     }
>    }
>   }
>  }
>  this.getResponse = function() {
>   if(xhr.responseText) {
>    return xhr.responseText;
>   }
>  }
>  this.onTimerEvent = function() {
>   send();
>  }
>  var self = this;
>  var stopped = false;
>  var originalDecay = decay || 1.2;
>  decay = originalDecay;
>  var xhr = createRequestObject();
>  var lastResponse = "";
>  this.start();
> }
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