javascript - Why TypeError after adding properties to an observable object in knockout.js? -

i playing around building custom handler adds new observablearray-properties parts of myviewmodel make sure nested templates within elements bound handlers have right arrays - see jsfiddle full example.

<div data-bind="contentavailable: ['children','pos1']">     <div data-bind="template: { name: 'default', foreach: children().pos1 }"> </div> 

within handler checked if current object bindingcontext.$data had observable object property name valueaccessor()[0] (in example 'children') , if observable object in turn had observable array of it's own name valueaccessor()[1] ('pos1') - , in case of absence assing them.

at first tried valuehasmutated() , reseting observable shown here

//within handler bindingcontext.$data[valueaccessor()[0]]()[valueaccessor()[1]]=ko.observablearray([]); //and after ko.applybindings(myviewmodel)  child1.children().pos1().push(new viewchild(2)); child1.children().pos1.valuehasmutated(); 

this almost-worked - since didn't want notify mutation every time push value tried place valuehasmutated() within handler - after adding observablearray() result in uncaught typeerror: object not function (tho typeof 1 line above says otherwise xd ).

am using object refrences in fundamentally wrong way or lacking understanding in how knockout it's magic? :d

still kind of digesting trying do, noticed have typo have i(1) instead of i[1] in typeof check in binding handler:

if(!bc.$data[i[0]]().hasownproperty(i[1]) || typeof bc.$data[i[0]]()[i(1)] !== 'function'){                    var existing = bc.$data[i[0]]();