Try two download links without user interaction in Javascript or HTML5

My problem is as follows:

I serve a webpage to clients that contains two different download links to the same file. I want the client(!) to test both wi开发者_开发百科thout manually clicking both links (I still present them both as a fail safe). Can this be done with javascript or html5?

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What you can do is making an HTTP HEAD request and look at the status code. The status code tells you whether the resource is available, while a HEAD request does not fetch the resource contents itself.

This can be done with AJAX, depending on your framework.

E.g. with jQuery:

$.ajax({ type: "HEAD",
         url: "download_url",
         complete: function(xhr) {
             if(xhr.status === 200) { /* is  available */ }
             else                   { /* not available */ }
         }
});

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Set location = "some URL" twice.

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Try this:

<img src="providerSrc" onerror="this.src=fallbackSrc" onabort="this.src=fallbackSrc" />

Customized to your needs of course...