How To Verify Webpage Exists

I have the following script that auto-submits a form at intervals.

setTimeout("document.forms['pageReloader'].submit();",90000);

Unfortunately, sometimes the target webpage is not available and I get
"page not found". That immediately kills my application, until I manually
restart it.

Is there a way in javascript to first check if a link exists before the
form is submitted?

For php programmers, an example of what I want will be:

if(fopen("http://www.example.com/", "r") {
do something here...
}