Knockout binding for cut text to the required length. It is a require js module. If it less then specified length then cut it and concatenate the trailing to the end of string.

knockout-cuttext

define(['knockout'],function(ko){
      ko.bindingHandlers.cuttext = {
              update: function (element, valueAccessor,allBindingsAccessor) {
                  var length = allBindingsAccessor().length || 4294967295; //SAFE MAX_INT
                  var trailing = allBindingsAccessor().trailing || "";
                  var value = ko.utils.unwrapObservable(valueAccessor());
                  if (length<value.length){
                       value = value.substr(0,length)+trailing;
                  }
                  $(element).text(value);
              }
      };
};
/*
  Examples: 
  with trailing:
   <div data-bind="cuttext:yobservable , length: 300, trailing:'...'"></div>
   without trailing:
   <div data-bind="cuttext:yobservable , length: 300"></div>
*/