async-6.js

function httpGetJson(url) {
    return spawn(function* () {
        // check if the URL looks like a JSON file and call httpGet.
        var regex = /\.(json)$/i;

        if (regex.test(url)) {
            // call the async function, wait for the result
            return yield httpGet(url);
        } else {
            throw Error('Bad Url Format');
        }
    }, this);
}