Unable to create Rx.Observable from JS event

I'm trying to figure out how to use rx.js with a dog-simple example, but can't figure out what reference or file I'm missing that means it isn't working.

<!DOCTYPE html>
<html>
<head>
    <title>Empty</title>
    <script src="/Scripts/rx.js"></script>
</head>
<body>
    <script>
        var thing = Rx.Observable.fromEvent(document, 'keydown');
    </script>
</body>
</html>

That's literally it. The script line correctly loads a local copy of rx.js 2.4.1 freshly downloaded from nuget.

I'm getting the error Rx.Observable.fromEvent is not a function, so I'm assuming that there is a missing reference.

It might just be the time of night, but I'm struggling to see what I'm doing wrong. Any help?

Solution

Resolved by downloading and using additional Rx files rx.async.js and rx.binding.js like so:

<!DOCTYPE html>
<html>
<head>
    <title>Empty</title>
    <script src="/Scripts/rx.js"></script>
    <script src="/Scripts/rx.async.js"></script>
    <script src="/Scripts/rx.binding.js"></script>
</head>
<body>
    <script>
        var thing = Rx.Observable.fromEvent(document, 'keydown');
    </script>
</body>
</html>