Identify network error in Javascript

Question

Context:

---

Writing a browser based tool that hits a number of 3rd party URLs to see if we can hit that URL or not

Constraints

1. Has to be browser based 
2. I don't own the URL list (read it from a server and is maintained by someone else )
3. Some of the URLs (ie the servers) are not CORs enabled.

Traditionally, I would have used XMLHttpRequest and done something like this to see if there are Network Errors. However, since these are cross domain requests, and hence fail at pre-flight step.

What I have done so far is a hack. Here is the code. Basically dynamically creating a script tag, with src as the url I want to get.

var createScript = function(whitelist){
    var src = whitelist.url;
    var script = document.createElement('script');
    script.setAttribute('src', src);
    script.onload = function () {

        whitelist.success = true;
        $scope.$digest();
        return;
    };
    script.onerror = function (foo) {
            console.error(src,' ',foo);
        return;
    };
    angular.element(document.body).append(script);
};

Ive looked at the object being passed to the onerror but Ive not been able to get anything useful from it , which would help me understand why this failed. Also, both network errors and 403s both hit the onerror handler. For my purposes, success or failure to access a url is determined by network errors as opposed to getting for example a 403.

Question

With the given constraints is there a way I can identify success or failure. Success or failure as far as Im concerned is whether you can access a URL or not.

Answer 1

I ended up writing an installable chrome-app and a chrome extension for this. Either one can be used depending on your use case. The chromme extension is more if you want to use this same functionality from a 3rd party web page.

https://github.com/sajit/clienthealthcheck <-- chrome app

https://github.com/sajit/healthcheck_api <-- chrome extension