new_gist_file_0

var originalPush = Array.prototype.push;

var Arr = function() {
  var constr = new Array.prototype.constructor;
  originalPush.apply(constr, arguments);
  constr.events = [];
  return constr;
};

Arr.prototype = Array.prototype;

Arr.prototype.events = [];

Arr.prototype.on = function(eventName, handler) {
  this.events.push({
    name: eventName,
    handler: handler
  });
};

Arr.prototype.trigger = function(eventName, args) {
  args = args || [];

  for (var i=0,len=this.events.length; i<len; i++) {
    if (this.events[i].name == eventName) {
      this.events[i].handler.apply(this, [args]);
    }
  }
};

Arr.prototype.walk = function(handler) {
  var oldValue, newValue;
  var items = [];

  for (var i=0,len=this.length; i<len; i++) {
    oldValue = this[i];
    newValue = handler.apply(this, [oldValue, i]);
    
    if (typeof newValue !== 'undefined') {
      this[i] = newValue;
      items.push({
        index: i,
        oldValue: oldValue,
        newValue: newValue
      });
    }
  }

  this.trigger('changed', {
    type: 'walk',
    items: items
  });

  return this;
};

Arr.prototype.push = function() {
  var result = originalPush.apply(this, arguments);
  this.trigger('changed', {
    type: 'push',
    length: result,
    args: arguments
  });
  return result;
};

var a = new Arr(1, 2, 3);

a.on('changed', function(e) {
  console.log(e);
});

console.log(a);