javascript - Knockoutjs does not update viewmodel -

in view have file input:

<input type="file" class="file-input" name="file_source" size="40"  onchange=''> 

and span, in showing uploaded filename:

<span class='label label-info' id="upload-file-info" data-bind="text: image"></span>  $(".file-input").change(function() {            var elem = $("#upload-file-info");            elem.html = $(this).val();         }); 

this span binded knockoutjs:

viewmodel = { image: ko.observable() }  ko.applybindings(viewmodel); 

the problem observable not updates when update span text. althought have filename in span, observable empty. how can make observable update when span text changes ?

i did quick fiddle according comment on question. should work:

jquery(document).ready(function ($) {     'use strict';      $(".file-input").change(function () {         var elem = $("#upload-file-info");         viewmodel.image($(this).val());     });      var viewmodel = {         image: ko.observable()     };     viewmodel.image.subscribe(function (value) {         alert(value);     });      ko.applybindings(viewmodel); });