// This function will parse HTTP GET string for variable/value pairs
    function parseQueryString(str) {
     str = str ? str : location.search;
     var query = str.charAt(0) == '?' ? str.substring(1) : str;
     var args = new Object();
     if (query) {
      var fields = query.split('&');
      for (var f = 0; f < fields.length; f++) {
       var field = fields[f].split('=');
       args[unescape(field[0].replace(/\+/g, ' '))] = unescape(field[1].replace(/\+/g, ' '));
      }
     }
     return args;
    }
    
    // Ok, let's make args array globally availabe
    var args = parseQueryString();
    
    // This function will autofill form fields values
    function autofill() {
        if (args['listing'])
            document.forms.namedItem('my_form').elements.namedItem('listing').value = args['listing'];
    }