gistfile1.js

new YAHOO.util.XHRDataSource(url, {
    responseType: YAHOO.util.DataSource.TYPE_JSON,
    responseSchema: {
        resultsList: 'Results',
        fields: [ 'foo', 'bar', 'baz' ]
    }
}).sendRequest(queryString, {
    // handler that will execute when the XHR returns
    success: function (req, res, payload) {
        /* here's where you access the results from res.results */
    },

    // handler that will execute if the XHR fails
    failure: function (req, res, payload) {
    },

    // object that is returned into the success/failure handler
    argument: /* if you need transaction specific stuff sent to your callbacks */ null
});