How to create a function with return value in knockoutjs

Question

this is my itemModel:

var itemModel = function (id,description,picture,totalInventory,retailPrice,dealerPrice,category,brand,unitOfMeasure,createdBy,status,highestCost, lowestCost) {
var self = this;

self.ID = ko.observable(id);
self.Description = ko.observable(description);
self.Picture = ko.observable(picture);
self.TotalInventory = ko.observable(totalInventory);
self.RetailPrice = ko.observable(retailPrice);
self.DealerPrice = ko.observable(dealerPrice);
self.Category = ko.observable(category);
self.Brand = ko.observable(brand);
self.UnitOfMeasure = ko.observable(unitOfMeasure);
self.CreatedBy = ko.observable(createdBy);
self.Status = ko.observable(status);
self.HighestCost = ko.observable(highestCost);
self.LowestCost = ko.observable(lowestCost);};

I have this method to get the items

self.GetItems = function(){
   $.getJSON("/Items/GetItems",{status: self.ItemStatus()}, function (result) {
      for (var i = 0, j = result.data.length; i < j; i++){
            item = result.data[i];
            underlyingArray.push(new itemModel(
                item.ID,
                item.Description,
                item.Picture,
                ....computetotalinventoryhere...,
                item.RetailPrice,
                item.DelearPrice,
                item.Category,
                item.Brand,
                item.UnitOfMeasure,
                item.CreatedBy,
                item.Status,
                item.HighestCost,
                item.LowestCost
            ));
        }
        self.list.valueHasMutated();
   }

};

I want to create a function to compute the total inventory. Is that possible in knockout? or any suggestion on how to do this. thanks.

Where does underlyingArray variable come from? Are your missing an assignment before the for loop ? Is the total across ALL items in "self.list" or does each itemModel have its own total value — Robert Slaney
– Robert Slaney, Commented Mar 4, 2014 at 2:09
above that i set the variables var item, underlyingArray = self.list(); — comfreakph
– comfreakph, Commented Mar 4, 2014 at 3:28
What about the other questions... it could influence the answer — Robert Slaney
– Robert Slaney, Commented Mar 4, 2014 at 3:48

QBM5 · Accepted Answer · 2014-03-04 01:25:33Z

2

Use a computed observable

var totalInv = ko.computed(function(){
   var total = 0;
   for(var i = 0; i < underlyingArray().length; i++){
       total += underlyingArray()[i].RetailPrice; // OR OTHER VALUES AS NEEDED
   }

   return total;  // or other values as needed
});

answered Mar 4, 2014 at 1:25

QBM5

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1 Comment

Robert Slaney Over a year ago

If you have to luxury of ES5 I suggest the use of map/reduce instead of for loop with external total variable "return underlyingArray().map(~selectorFn~).reduce( function(prev, curr) { return prev + curr; }, 0)

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