HTML Search using MVVM with knockout.js

<!DOCTYPE html>
<html>
<head>
    <script type="text/javascript" src="http://code.jquery.com/jquery-latest.pack.js"></script>
    <script type="text/javascript" src="http://knockoutjs.com/downloads/knockout-3.0.0.js"></script>
     
    <script type="text/javascript" >
        $(function(){
         
            // custom binding handler so pressing enter in a textbox is the same
            // as clicking the button.
            ko.bindingHandlers.enterKey = {
                init: function(element, valueAccessor, allBindings, vm) {
                    ko.utils.registerEventHandler(element, "keyup", function(event) {
                        if (event.keyCode === 13) {
                            ko.utils.triggerEvent(element, "change");
                            valueAccessor().call(vm, vm);
                        }                        
                        return true;
                    });
                }         
            };
         
            var fakeSearch = function(args, callback) {
                var data = args;
                callback(data);
                return args;
            };

            var ButtonViewModel = function(text, searchMethod, canSearchMethod) {
                var _self = this;
                _self._canSearchMethod = canSearchMethod;
                _self.text = ko.observable(text);
                _self.onClick = searchMethod;
                _self.canClick = ko.computed(_self._canSearchMethod);                
            };

            var SearchParametersViewModel = {
                'SearchTerm': ko.observable(''),
                'SearchOption': ko.observable(''), // Not used in example
                'StartDate': ko.observable(''),    // Not used in example
                'EndDate': ko.observable('')       // Not used in example
            };

            var SearchViewModel = function(searchMethod, searchArgs) {
                // private properties
                var _self = this;
                _self._searchMethod = searchMethod;
                _self._searchArgs = searchArgs;
                _self._canSearch = function() {
                    return _self.searchParameters.SearchTerm() != null && _self.searchParameters.SearchTerm() != '';
                };

                // public properties
                _self.searchParameters = SearchParametersViewModel;

                _self.results = ko.observable('');
                
                _self.searchCallBack = function (data) {
                    _self.results(JSON.stringify(data));
                };

                _self.searchButton = new ButtonViewModel("Search", 
                function () {
                    _self._searchMethod(_self._searchArgs, _self.searchCallBack);
                }, _self._canSearch);
                
            };
           
          ko.applyBindings(new SearchViewModel(fakeSearch, {a: "1", b: "2"}));
        });
    </script>
</head>
<body>
    <input data-bind="value: searchParameters.SearchTerm, valueUpdate: 'afterkeydown', enterKey: searchButton.onClick" />
    <button type="button" id="btnSearch" data-bind="text: searchButton.text, enable: searchButton.canClick, click: searchButton.onClick"></button>
    <p data-bind="text: results"></p>
</body>
</html>

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