Observer pattern implementation in JavaScript

observer.js

function Click() {
  this.handlers = [];  // observers
}
 
Click.prototype = {
 
  subscribe: function(fn) {
    this.handlers.push(fn);
  },
 
  unsubscribe: function(fn) {
    this.handlers = this.handlers.filter(
      function(item) {
        if (item !== fn) {
          return item;
        }
      }
    );
  },
 
  fire: function(o, thisObj) {
    var scope = thisObj || window;
    this.handlers.forEach(function(item) {
      item.call(scope, o);
    });
  }
}
 
// log helper
 
var log = (function() {
  var log = "";
 
  return {
    add: function(msg) { log += msg + "\n"; },
    show: function() { alert(log); log = ""; }
  }
})();
 
function run() {
 
  var clickHandler = function(item) { 
    log.add("fired: " + item); 
  };

  var click = new Click();

  click.subscribe(clickHandler);
  click.fire('event #1');
  click.unsubscribe(clickHandler);
  click.fire('event #2');
  click.subscribe(clickHandler);
  click.fire('event #3');

  log.show();
}