How can I, using Knockout on Sharepoint, have a div visable when a value from a list is clicked on a dropdown?

Question

Application: 
<select data-bind="value: $data.selectedApp, options: $parent.applications, optionsText: 'ApplicationName', optionsCaption: 'Choose an Application'" style="width: 32px" name="Application list" id="dataBox">
</select>

With this I'm trying to make

<Div = "main">...</div>     

visable when a dropdown called "USB Access Request" is clicked.
My javascript:

<script>
    var viewModel = {
        selectedChoice: ko.observable("USB Read/Write") ,
        selectionChanged: function(event) {
            show( "main" );  
        } 
    };
    ko.applyBindings(viewModel);   
</script>

Answer 1

You might be looking for something like this

View model:

   var viewModel = function () {
       var self = this;
       self.selectedApp = ko.observable();
       self.applications = ko.observableArray([{
           "ApplicationName": "application1"},{
               "ApplicationName": "application2"},{
                   "ApplicationName": "application3"}
       ]);
   };
   ko.applyBindings(new viewModel())

View :

Application:
<select data-bind="value:selectedApp,options:applications,optionsText:'ApplicationName',optionsCaption:'Choose an Application'" style="width: 160px"></select>

<div data-bind="if:selectedApp">
     <h2>i'm Main DIV</h2>
</div>

Well i see the html is simple so its always better to use if binding in this case .

Working fiddle here

Any issues let us know