Implementing a Cross-Domain Request for JSON Data

In this example, we begin with a YUI instance that loads the io-xdr, json-parse, and node modules. The io-xdr module is the key module. The other modules are used to process and output the results:

//Create a YUI instance including support for IO and JSON modules:
YUI().use("io-xdr", "json-parse", "node", function(Y) {
    // Y is the YUI instance.
    // The rest of the following code is encapsulated in this
    // anonymous function.
});

We'll also get a Node reference to the container we'll be using to output the data we retrieve:

//element #output:
var output = Y.one("#output ul");

handleSuccess is the function responsible for handling the response data. The first thing we do is sanitize the data to ensure we have valid JSON.

var oRSS = Y.JSON.parse(o.responseText);

Next, we create a simple markup template and use Y.Lang.sub() to fill in the data, as we iterate through the JSON and output the results.

//From here, we simply access the JSON data from where it's provided
//in the Yahoo! Pipes output:
if (oRSS && oRSS.count) {
    var s = "<!--begin news stories fetched via Yahoo! Pipes-->",
        //t in this case is our simple template; this is fed to
        //Y.Lang.sub() as we loop through RSS items:
        t = "<li><a href='{link}'>{title}</a>, {pubDate}</li>";

    for (var i=0; i<oRSS.count; i++) {
        s += Y.Lang.sub(t, oRSS.value.items[i]);
    }

    //Output the string to the page:
    output.set("innerHTML", s);
    output.addClass("yui-null");
}

Create the configuration object for the cross-domain request, setting up the event handlers and instructing IO to use the browser's native cross-domain transport.

var cfg = {
    method: "GET", //If omitted, the default is HTTP GET.
    xdr: {
        use:'native'//For browsers that support CORS.
    },
    on: {
        //Our event handlers previously defined:
        start: handleStart,
        success: handleSuccess,
        failure: handleFailure
    }
};

Create an event handler that will make the IO call to Yahoo! Pipes when the Load button is clicked:

//Wire the button to a click handler to fire our request each
//time the button is clicked:
var handleClick = function(o) {
    Y.log("Click detected; beginning io request to Yahoo! Pipes.", "info", "example");
    // Remove the default "X-Requested-With" header as this will
    // prevent the request from succeeding; the Pipes
    // resource will not accept user-defined HTTP headers.
    Y.io.header('X-Requested-With');
    var obj = Y.io(
	//this is a specific Pipes feed, populated with cycling news:
	"http://pipes.yahooapis.com/pipes/pipe.run?_id=giWz8Vc33BG6rQEQo_NLYQ&_render=json",
	cfg
    );
}

//add the click handler to the Load button.
Y.on("click", handleClick, "#pipes");

Full Script

The full script source for this example is as follows:

<button id="pipes">Load RSS news feed from Yahoo! Pipes.</button>
<div id="output">
    <ul>
        <li>Content from Yahoo! Pipes feed will display here.</li>
    </ul>
</div>

<script language="javascript">
YUI({ filter:'raw' }).use("io-xdr", "json-parse", "node",
    function(Y) {

        //Data fetched will be displayed in a UL in the
        //element #output:
        var output = Y.one("#output ul");

        //Event handler called when the transaction begins:
        var handleStart = function(id, a) {
            Y.log("io:start firing.", "info", "example");
            output.set("innerHTML", "<li>Loading news stories via Yahoo! Pipes feed...</li>");
        }

        //Event handler for the success event -- use this handler to write the fetched
        //RSS items to the page.
        var handleSuccess = function(id, o, a) {

            //We use JSON.parse to sanitize the JSON (as opposed to simply performing an
            //JavaScript eval of the data):
            var oRSS = Y.JSON.parse(o.responseText);

            //From here, we simply access the JSON data from where it's provided
            //in the Yahoo! Pipes output:
            if (oRSS && oRSS.count) {

                var s = "<!--begin news stories fetched via Yahoo! Pipes-->",
                    //t in this case is our simple template; this is fed to
                    //Y.Lang.sub() as we loop through RSS items:
                    t = "<li><a href='{link}'>{title}</a>, {pubDate}</li>";

                for (var i=0; i<oRSS.count; i++) {
                    s += Y.Lang.sub(t, oRSS.value.items[i]);
                }

                //Output the string to the page:
                output.set("innerHTML", s);
                output.addClass("yui-null");

            } else {
                //No news stories were found in the feed.
                var s = "<li>The RSS feed did not return any items.</li>";
            }
        }

        //In the event that the HTTP status returned does not resolve to,
        //HTTP 2xx, a failure is reported and this function is called:
        var handleFailure = function(id, o, a) {
            Y.log("ERROR " + id + " " + a, "info", "example");
        }

        //With all the apparatus in place, we can now configure our
        //IO call.  The method property is defined, but if omitted,
        //IO will default to HTTP GET.
        var cfg = {
            method: "GET",
            xdr: {
                use:'native'
            },
            on: {
                //Our event handlers previously defined:
                start: handleStart,
                success: handleSuccess,
                failure: handleFailure
            }
        };

        //Wire the button to a click handler to fire our request each
        //time the button is clicked:
        var handleClick = function(o) {
            Y.log("Click detected; beginning io request to Yahoo! Pipes.", "info", "example");
	    // Remove the default "X-Requested-With" header as this will
	    // prevent the request from succeeding; the Pipes
	    // resource will not accept user-defined HTTP headers.
	    Y.io.header('X-Requested-With');
            var obj = Y.io(
                //this is a specific Pipes feed, populated with cycling news:
                "http://pipes.yahooapis.com/pipes/pipe.run?_id=giWz8Vc33BG6rQEQo_NLYQ&_render=json",
                cfg
            );
        }

        //add the click handler to the Load button.
        Y.on("click", handleClick, "#pipes");
    }
);
</script>