knockout.js - Why does adding a computed to an observableArray fail? -

i think wrong here. add ko.computed ko.observablearray this.

before model clarity

//var job = @html.raw(json.encode(model.job)); //var customer = @html.raw(json.encode(model.customer)); //var estimatematerials = @html.raw(json.encode(model.estimatematerials)); //var estimate = @html.raw(json.encode(model.estimate)); var estimatetasks = @html.raw(json.encode(model.tasks));  var jobpostviewmodel = function(){     var self = this;     //self.customer = ko.observable(customer);     //self.job = ko.observable(job);     //self.estimatematerials = ko.observablearray(estimatematerials);     //self.estimate = ko.observable(estimate);     self.estimatetasks = ko.observablearray(estimatetasks);     self.estimatetasks().estlaborsubtotal = ko.computed(function () {         return (isnan(self.esthr)? 0: +self.esthr) * (isnan(self.taskperhourcost)? 0: +self.taskperhourcost);     }); }; var model = new jobpostviewmodel(); ko.applybindings(model,  document.getelementbyid("my_job_form")); 

so model bind is. my_job_form data-bind="with:jobs" , populating table inside form bound estimatetasks. markup is

<tbody data-bind="foreach: $root.estimatetasks">     <tr>         <td>             <input type="text" data-bind="value: esthr" />             <input type="hidden" data-bind="value: taskperhourcost" />         </td>         <td>             <input type="text" data-bind="value: estlaborsubtotal" disabled />         </td>     </tr> </tbody> 

on bind, error

referenceerror: estlaborsubtotal not defined

what doing wrong here?

you adding computed array. array result of evaluation of estimatetasks observablearray();

if understand trying do.

you better way. add computed named estlaborsubtotal item.

var jobpostviewmodel = function(){     var self = this;     ko.utils.arrayforeach(estimatetasks, function(et) {         et.estlaborsubtotal  = ko.computed({             read: function(){                 var esthr = this.esthr();                 var taskperhourcost =  this.taskperhourcost();                 if(esthr === null)                     return 0;                 return esthr * taskperhourcost;              },             owner : et // specify "this" during evaluation          });     });      self.estimatetasks = ko.observablearray(estimatetasks); }; 

see fiddle

i hope helps.