knockout.js - Why isn't my knockout observable property, and boud input field being updated? -

i have object observable properties.

this.usertoadd = {         id: ko.observable(""),         firstname: ko.observable(""),         lastname: ko.observable(""),         active: ko.observable(""),         email: ko.observable(""),         roles: ko.observablearray([])     }; 

i attempt update object when button clicked

$(document).on("click", ".edit", function () {      var itemtoupdate = ko.datafor(this);      if (itemtoupdate.id !== undefined) {         //update observable         vm.usertoadd.id = itemtoupdate.id;         vm.usertoadd.firstname = itemtoupdate.firstname;         vm.usertoadd.lastname = itemtoupdate.lastname;         vm.usertoadd.email = itemtoupdate.email;         vm.usertoadd.active = itemtoupdate.active;         vm.usertoadd.roles = itemtoupdate.roles;         //update form, , there must better way         $('input[name="id"]').val(itemtoupdate.id);         $('input[name="firstname"]').val(itemtoupdate.firstname);         $('input[name="lastname"]').val(itemtoupdate.lastname);         $('input[name="email"]').val(itemtoupdate.email);         $('input[name="active"]').val(itemtoupdate.active);           } }); 

it runs because see input fields being updated values expect, model not updated. doing wrong? also, had use

$('input[name="id"]').val(itemtoupdate.id); 

to update input field

<input name="id" type="text" placeholder="id" data-bind="value: id, valueupdate: 'afterkeydown'" />          

because value of input field not update when observable property updated. can help?

the ko.observable call returns function. set value need call new value argument:

vm.usertoadd.id(itemtoupdate.id); vm.usertoadd.firstname(itemtoupdate.firstname); vm.usertoadd.lastname(itemtoupdate.lastname); vm.usertoadd.email(itemtoupdate.email); vm.usertoadd.active(itemtoupdate.active); vm.usertoadd.roles(itemtoupdate.roles); 

for further reading: reading , writing observables:

to write new value observable, call observable , pass new value parameter. example, calling myviewmodel.personname('mary') change name value 'mary'.