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aport

Member

From: San Diego

Registered: 2008-02-20

Posts: 99

Array of XMLHttpRequests

I want to create an array of AJAX calls to validate a list of URLs.

var req=new Array(3);
var url=new Array(3);
url[0]="http://www.google.com";
url[1]="http://www.3.com";
url[2]="http://www.1.com";

function validate() {
    for(var i=0; i<3; i++) {
        req[i] = new XMLHttpRequest();
        req[i].onreadystatechange = function() {

            if(req[i].readyState == 4 && req[i].status == 200) {
                URL = url[i];
                success();
            } 

        }
        req[i].open("GET", url[i], true);
        req[i].send(null);    
    }

}

Basically what I want to do is validate these urls to find out which is live, and then do something with that live URL.

This code works on 4 of my computers. The fifth doesn't work. I debugged it as best as I could and found out that, even on a live URL, the line

if(req[i].readyState == 4 && req[i].status == 200) {

is evaluating as false.

If I create a different function, outside of an array, to validate this URL using the same method, it returns true.

What am I doing incorrectly here? Or is there a better way to make AJAX requests on an array of URLs?

mrunion

Member

From: Jonesborough, TN

Registered: 2007-01-26

Posts: 1,938

Website

Re: Array of XMLHttpRequests

I don't know why 1 of 5 is failing, but I would do this anyway to avoid confusion:

if ((req[i].readyState == 4) && (req[i].status == 200)) {

This is DEFINITELY only an opinion.

---

Matt

"It is very difficult to educate the educated."

mazzarelli

Member

Registered: 2008-08-27

Posts: 6

Re: Array of XMLHttpRequests

Unless I'm not understanding what you are doing, none of them should work. Browsers are built to specifically prevent cross-domain xhr.

aport

Member

From: San Diego

Registered: 2008-02-20

Posts: 99

Re: Array of XMLHttpRequests

Unless I'm not understanding what you are doing, none of them should work. Browsers are built to specifically prevent cross-domain xhr.

The code runs under a Vista gadget, which I guess doesn't have any issues doing it because the requests are successful.

ssjlegendx

Member

Registered: 2008-01-01

Posts: 94

Website

Re: Array of XMLHttpRequests

Perhaps it's a scoping issue?

I'm not an expert on scope in JavaScript, but I'd be fearful of the references into req within the onreadystatechange function.

---

#!/vim/rocks

aport

Member

From: San Diego

Registered: 2008-02-20

Posts: 99

Re: Array of XMLHttpRequests

Perhaps it's a scoping issue?

I'm not an expert on scope in JavaScript, but I'd be fearful of the references into req within the onreadystatechange function.

You were right, it was a scope/close issue.
The value of i in the onreadystate function was not what I was expecting.

By closing it, it worked like a charm:

var req=new Array(3);
var url=new Array(3);
url[0]="http://www.google.com";
url[1]="http://www.3.com";
url[2]="http://www.1.com";

function validate() {
    for(var i=0; i<3; i++) {
        req[i] = new XMLHttpRequest();
        req[i].onreadystatechange = function(index) {
                  return function() {
                        if(req[index].readyState == 4 && req[index].status == 200) {
                        URL = url[index];
                        success();
                       }
            };
        }(i);
        req[i].open("GET", url[i], true);
        req[i].send(null);    
    }

}