Declaring javascript object in a js file.

Question

I want to declare a object in a js file like: var o = {p:1};

and then create a watch for it in my html file.

  <script>

  var o = {p:1}; 

  o.watch("p",function (id, oldval, newval)
  { 


  alert(newval);
  return newval; 
  }); 

  o.p=count;
  </script>

this code works in my html but if I declare "var o' in my js file it does not work. The reason I want to do that is because a I want to modify the value of my object in my js file and detect it in the html.

Answer 1

The only approach I can think of to track changes to object vars is to use a setter func instead of updating the value directly:

<script type="text/javascript">
  var o = { 
    p:1,
    q:0,
    watches: [],
    setProp: function(prop, newVal) {
      var oldVal = this[prop];
      this[prop] = newVal;
      if(typeof(this.watches[prop]) == 'function')
      {
         this.watches[prop](prop, oldVal, this['prop']);
      }
    }
  }; 

  o.watches["p"] = function (id, oldval, newval) {
    alert(newval);
    return newval; 
  }; 

  o.setProp('p', count);
  o.setProp('q', 0 - count);
</script>

This is about the simplest thing I can come up with, though you'd probably want to add some better error-checking or maybe an addWatch(prop, func) method to o.