knockout.js - Accessing knockout js selected option inside a computed variable -


i want create computed observable return percentage value:

self.percentage = ko.computed(function(){             var percentage = (self.amount() * self.selecteditem().itemvat)/100;             return percentage;         });

i keep getting - uncaught typeerror: cannot read property 'itemvat' of undefined.

var items = function(item_name, item_number, item_vat) {         this.itemname = item_name;         this.itemnumber = item_number;         this.itemvat = item_vat;     };

an ajax call used create new items , assign them select box using options binding following:

this.availableitems = ko.observablearray(); this.selecteditem = ko.observable();  jquery.each(data, function(i, val) {                     self.availableitems .push(new items(val.item_name,val.item_number,val.item_vat));                 });   <select class="form-control" name="item_name" id="item_name" data-bind = "options: availableitems,                        optionstext: 'itemname',                        value: selecteditem,                        optionscaption: 'choose...'"></select>

by specifying optionscaption, allow selecteditem undefined. test that, , you're ok.

  self.percentage = ko.computed(function() {     if (self.selecteditem() === undefined) return 0;     var percentage = (self.amount() * self.selecteditem().itemvat) / 100;     return percentage;   });

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