title: "this[key]" on a for() in javacscript with prototype
body: <p>I've a JS error on the 5th line of this script (var el = this[key];). It works on FF, Chrome, Safari but not on IE. Someone can help me ? </p>
  
  <pre><code>Object.prototype.between = function( value )
  {
      var value = parseFloat(value);
      for (key in this) {         
          var el = this[key];
          var v = key.split('-');         
  
          var min = parseFloat(v[0]);
          var max = parseFloat(v[1]);
  
          if (value &gt;= min &amp;&amp; value &lt; max) { return el; }
      }
      return false;
  }
  </code></pre>
  
  <p>Thanks for advance</p>