Clevar constructs an accessor function that retains its own History Store and keeps the value absolutely private. Neat utility for tracking history of a variable over time.

Clevar.js

var Clevar = function(value){
  // Constructs an accessor function that retains its own History Store.
  var _this = this;
  var _history = [];                 // Indexable history (newest to oldest)

  // Define static objects, only the first time Clevar is run.
  Clevar.Record = Clevar.Record || function(value){
    this.created = new Date();
    this.value = value;
  };

  Clevar.Record.prototype.getFormatted =  Clevar.Record.prototype.getFormatted || function(next){
    return 'Value was ' + this.value + ', created at ' + this.created.toUTCString() + (next ? ' and changed at ' + next.created.toUTCString() : '');
  };

  var Record = Clevar.Record;  // Reference to static object - reduce scope lookup.
  var _current = value ? new Record(value) : new Record(null);        // Current value

  return function(value, index/* Only for use with exploring history */){
    // Value should be able to be 0 or null and go on record.
    if(value !== undefined){  // SET

      // User is requesting history of Clevar instance. If index provided does not exist, returns all records for user to sort through.
      if(value === '__history'){ return (index !== undefined && typeof _history[index] === 'object') ? _history[index].getFormatted(typeof _history[index + 1] === 'object' ? _history[index + 1] : null) : _history; }

      // Need to perform a deep clone on objects, otherwise passed by reference. Save for a more clevar solution.
      // If you have jQuery, prototype, or anything with an extend/deep clone function, this would be the place to use it.
      if(_current.value instanceof Object && typeof $.extend === 'function'){
        _history.push($.extend({}, _current));
      } else {
        // Otherwise, no deep clone.
        _history.push(_current);
      }

      // Set new current value.
      _current = new Record(value);

    } else {  // GET
      return _current.value;
    }
  }
};


/*

USAGE:

  // Declare.
  var a = new Clevar('hello');
  
  // Set.
  a('world');
  a(20);
  
  // Get.
  a();                                // -> world
  
  // Full history.
  a('__history');                     // -> [Record, Record, Record]
  
  // History by index.
  a('__history', 2);                  // -> Informative string.

*/