jquery - Knockout $root binding does not update UI element immediately -

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i want display $root on page know what's in object. after first add event, added item added object, ui not reflect change. on second add event, first item displayed on ui, second 1 not displayed until third add event , forth.

jsfiddle

html

<input type='text' data-bind='value: selecteditem' /> <input type='button' data-bind='click: additem' value='add' /> <pre>vm = <span data-bind="text: ko.tojson($root, null, 4)"></span></pre>

js

$(document).ready(function () {     var basevm = function () {         var = {};         return that;     };     var testvm = function () {         var = basevm();         that.relateditems = ko.observablearray(['pork', 'ham']);         that.selecteditem = ko.observable('');         that.additem = function () {             if (that.relateditems().indexof(that.selecteditem()) >= 0) {                 alert('existed');             } else {                 that.relateditems().push(that.selecteditem());             }         };         that.removeitem = function () {             if (that.relateditems().indexof(that.selecteditem()) >= 0) {                 that.relateditems().remove(that.selecteditem());             }         };         return that;     };     var vm = testvm();     ko.applybindings(vm); });

you're calling .push (and .remove) on underlying javascript array, knockout doesn't see change. it's when else causing whole thing rerender picks changes.

knockout redefines array functions on observablearrays, , when call them on objects, both updates underlying array , notifies subscribers. instead of this:

that.relateditems().push(that.selecteditem());

you need this:

that.relateditems.push(that.selecteditem());

here changes:

$(document).ready(function () {      var basevm = function () {          var = {};          return that;      };      var testvm = function () {          var = basevm();          that.relateditems = ko.observablearray(['pork', 'ham']);          that.selecteditem = ko.observable('');          that.additem = function () {              if (that.relateditems().indexof(that.selecteditem()) >= 0) {                  alert('existed');              } else {                  that.relateditems.push(that.selecteditem());              }          };          that.removeitem = function () {              if (that.relateditems().indexof(that.selecteditem()) >= 0) {                  that.relateditems.remove(that.selecteditem());              }          };          return that;      };      var vm = testvm();      ko.applybindings(vm);  });
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>  <script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>  <input type='text' data-bind='value: selecteditem' />  <input type='button' data-bind='click: additem' value='add' />  <pre>vm = <span data-bind="text: ko.tojson($root, null, 4)"></span></pre>


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