KnockoutJS caret binding

HTML

<script src="https://code.jquery.com/jquery-2.1.1.min.js"></script>
<script src="http://sukobuto.com/files/js/jquery.caret-1.5.2.min.js"></script>
<h1>KnockoutJS caret binding</h1>

<textarea data-bind="value: body, caret: bodyCaret"></textarea>

<p>caret pos: <span data-bind="text: bodyCaret"></span></p>
<button data-bind="click: insertFoo">insert Foo!</button>

CSS

textarea {
    width: 500px;
    height: 200px;
}

JavaScript

ko.bindingHandlers.caret = {
	init: function(element, valueAccessor, allBindings) {
		var $elm = $(element);
    var suspend = true;
    var value_writer = allBindings()._ko_property_writers.value;
        
    function updateModel() {
			var pos = $elm.caret();
			var modelValue = valueAccessor();
			suspend = true;
			if (ko.isObservable(modelValue)) modelValue(pos);
			else valueAccessor(pos);
		}

		$elm.bind('keydown click focus', updateModel);
		
		ko.computed(function() {
			var modelValue = ko.unwrap(valueAccessor());
			if (suspend) {
				suspend = false;
				if (typeof modelValue == 'number') return;
			}
			var st = element.scrollTop;
			$elm.caret(modelValue);
			element.scrollTop = st;
            if (typeof modelValue == 'string') {
                updateModel();
                if (value_writer) {
                    value_writer($elm.val());
                }
            }
		});
	}
};

function ViewModel() {
    var self = this;
    self.body = ko.observable("");
    self.bodyCaret = ko.observable(0);
    
    self.insertFoo = function() {
        self.bodyCaret("Foo!");
    }
}

var lipsum = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";

var vm = new ViewModel();
vm.body(lipsum);
ko.applyBindings(vm);