test.js

var loadScript = function(url, callback) {
    /*
    JavaScript that will load the jQuery library on Google's CDN.
    We recommend this code: http://snipplr.com/view/18756/loadscript/.
    Once the jQuery library is loaded, the function passed as argument,
    callback, will be executed.
    */

    var script = document.createElement("script");
    script.type = "text/javascript";

    if (script.readyState) {  //IE
        script.onreadystatechange = function() {
            if (script.readyState == "loaded" || script.readyState == "complete") {
                script.onreadystatechange = null;
                callback();
            }
        };
    } else {  //Others
        script.onload = function() {
            callback();
        };
    }

    script.src = url;
    document.getElementsByTagName("head")[0].appendChild(script);
};

var jqueryLoaded = function($) {
    $.ajax(
        '/admin/metafields.json', {
        dataType: 'json',
        complete: function(jqXHR, textStatus) {
            j = jqXHR.responseJSON;
            console.log(j);
        }
    });
};
  
if ((typeof jQuery === 'undefined') || (parseFloat(jQuery.fn.jquery) < 1.7)) {
    loadScript('//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js', function(){
        jQuery191 = jQuery.noConflict(true);
        jqueryLoaded(jQuery191);
    });
} else {
    jqueryLoaded(jQuery);
}