Set your checkbox to the value of an observable
<input type="checkbox" data-bind="checked: hasLimit" /></p>
Set your label bound to an KO computed
<label data-bind="text: someTextValue"></label>
And then have someTextValue be based on some other value in the view model
var hasLimit = ko.observable(true);
var someTextValue = ko.computed(function () {
var txtValue = historyItem.Note;
if (hasLimit) { return txtValue.Substring(0, 100) + "...";
return txtValue;
};
The above will start with a limit (and the checkbox will be checked) and then if the user unchecks the box it will show the entire text.