var config = {
    json: {
        baseUrl: "/some/url/$",
        getter: $.getJSON,
        validator: $.isPlainObject
    },
    template: {
        baseUrl: "/some/url/$.mustache",
        getter: $.get,
        validator: function (str) {
            return (/\{\{[a-zA-Z._]*\}\}/).test(str);
        }
    }
};

function getItem(itemOrName, type) {
    var result = $.Deferred(), cfg = config[type];
    if (cfg.validator(itemOrName)) {
        result.resolve(itemOrName);
    } else {
        cfg.getter(cfg.baseUrl.replace("$", itemOrName))
        .done(function (data) { result.resolve(data); })
        .fail(function (xhr) { result.reject(xhr); });
    }
    return result.promise();
}

var foo = {
    tmplReplaceContent: function (json, tmpl, target) {
        $.when(getItem(json, "json"), getItem(tmpl, "template"))
        .done(function (json, tmpl) {
            var content = Mustache.render(tmpl, json);
            $(target).html(content).hide().fadeIn();
        })
        .fail(function (xhr) {
            // show error message
        });
    }
};