gistfile1.js

// Sort stories by tasks progress
data.stories.data.sort(dynamicSortMultiple("!tasks.progress", "title", "priority"));

function dynamicSort(property) {
    return function(obj1, obj2) {
        var reverse = (property.indexOf("!") === 0);

        if (reverse) {
            property.substr(1);
        }

        if (property.indexOf(".") !== -1) {
            var bits = property.split(".");

            if (reverse) {
                return obj1[bits[0]][bits[1]] < obj2[bits[0]][bits[1]]
                    ? 1 : obj1[bits[0]][bits[1]] > obj2[bits[0]][bits[1]]
                    ? -1 : 0;
            } else {
                return obj1[bits[0]][bits[1]] > obj2[bits[0]][bits[1]]
                    ? 1 : obj1[bits[0]][bits[1]] < obj2[bits[0]][bits[1]]
                    ? -1 : 0;
            }
        } else {
            if (reverse) {
                return obj1[property] < obj2[property]
                    ? 1 : obj1[property] > obj2[property]
                    ? -1 : 0;
            } else {
                return obj1[property] > obj2[property]
                    ? 1 : obj1[property] < obj2[property]
                    ? -1 : 0;
            }
        }
    }
}

function dynamicSortMultiple() {
    /**
     * save the arguments object as it will be overwritten note that arguments object
     * is an array-like object consisting of the names of the properties to sort by
     */
    var props = arguments;

    return function (obj1, obj2) {
        var i = 0, result = 0, numberOfProperties = props.length;

        // try getting a different result from 0 (equal) as long as we have extra properties to compare
        while(result === 0 && i < numberOfProperties) {
            result = dynamicSort(props[i])(obj1, obj2);
            i++;
        }

        return result;
    }
}