Making and handling JSONP request using JavaScript

I would like to make cross domain request in the client end, so I chose JSONP. I am new to JSONP and would like to make a request to http://somedomain.com using JavaScript and not jQuery. It would be very helpful for my development if I get sample snippet to make and handle a request using JSONP in JavaScript.

Solution

Here's a small example fetching data from a google spreadsheet:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
   "http://www.w3.org/TR/html4/strict.dtd">

<html lang="en">
<head>
    <title>jsonp</title>
</head>
<body>
    <span></span>
    <script>
        //this function is the callback, it needs to be a global variable
        function readResponse(response){
            document.getElementsByTagName('SPAN')[0].innerHTML = response.feed.entry.length + ' entries returned';
            console.log(response);
        }
        (function(){
            //note the "readResponse" at the end
            var src = 'http://spreadsheets.google.com/feeds/list/o13394135408524254648.240766968415752635/od6/public/values?alt=json-in-script&callback=readResponse',
                script = document.createElement('SCRIPT');
            script.src = src;
            document.body.appendChild(script);
        })();

    </script>
</body>
</html>

One comment related to this example. If you want to play with your own google spreadsheet, you need to both share it as public, and publish it.