JSFiddle - React, Tailwind, and code Playground

JavaScript

/*****Change 1******/
/*Here is your sort function setup as a helper*/
var ArrayHelper = {
    sortBy : function(arr, prop){
        return function(){
            var so = srt.sortOrder == 'asc' ? 1 : -1;
            var key = srt.sortKey;
            var result = 0;
            console.log(srt.sortKey + ' ' + srt.sortOrder + ':');
            return function (a, b) {
                if (srt.isComputed) {
                result = (a[key]() < b[key]()) ? -1 : (a[key]() > b[key]()) ? 1 : 0;
                } else {
                    result = (a[key] < b[key]) ? -1 : (a[key] > b[key]) ? 1 : 0;
                }
                return result * so;
            };
        }
    }
};
/*****End Change 1******/

var rawData = [
  { "Id": 3, "itemCount": 3531, "val1": 905, "val2": 172 },
  { "Id": 2, "itemCount": 3111, "val1": 799, "val2": 147 },
  { "Id": 4, "itemCount": 3411, "val1": 871, "val2": 199 },
  { "Id": 5, "itemCount": 3414, "val1": 892, "val2": 178 },
  { "Id": 1, "itemCount": 3182, "val1": 845, "val2": 155 }
];



function MyItem(item) {
    var self = this;
    for (var val in item) {
      if (item.hasOwnProperty(val)) {
          self[val] = item[val];
      }
    }
 }

function extendMyItems() {
    MyItem.prototype.computedOne = function () {
        var input = this;
        return input.itemCount / input.val1;
    };

    MyItem.prototype.computedTwo = function () {
        var input = this;
        return input.val1 * input.val2;
    };
}

function getItems(input) {
    var ret = [];
    for (var i = 0; i < input.length; i++) {
        var item = new MyItem(input[i]);
        ret.push(item);
    }

    return ret;
}

function doIt() {

    Array.prototype.sortBy = function (property) {
        return this.sort(mySort(property));
    };

    extendMyItems();
    var sortList = [{ "sortKey": "Id", "sortOrder": "asc" },
                { "sortKey": "val1", "sortOrder": "asc" },
                { "sortKey": "val2", "sortOrder": "desc" },
              ...