anchor.diff:          var newState = {};
           newState[propPrefix + "Id"] = data.id;
           newState[propPrefix + "City"] = data.city;
  +        newState[propPrefix + "CityError"] = null;
           this.setState(newState);
           if (!data.city) { // retry until we get the city
             setTimeout(this.loadLocation, this.interval, path, propPrefix);
           }
         }.bind(this),
         error: function(xhr, status, err) {
  -        console.error(status, err.toString());
  -      }
  +        var errString = err.toString();
  +        var newState = {};
  +        newState[propPrefix + "CityError"] = errString;
  +        this.setState(newState);
  +        console.error(status, errString);
  +      }.bind(this)
       });
     },
   
     getInitialState: function() {
  -    return {};
  +    return {
  +      serverCity: "unknown location",
  +      serverCityError: null,
  +      clientCity: "unknown location",
  +      clientCityError: null
  +    };
     },
     componentDidMount: function() {
       this.loadLocation("/locations/current", "client");
  
positive.code: var ServerCity = React.createClass({
    render: function() {
      var city = this.props.city;
      if (!city) {
        city = "unknown location";
      }
      return (
        <span className="serverCity">{city}</span>
      );
    }
  });
  
negative.code:     ping.serverId = this.props.serverId;
      ping.clientId = this.props.clientId;
      return (
        <div>
          <form className="PingBox" onSubmit={this.handleSubmit}>
            <input type="submit" id="button" value={this.state.buttonValue} disabled={this.state.buttonDisabled} />
            <input type="text" placeholder="Median" id="ping_result_lag_ms" value={this.state.resultValue} size="5" readOnly />
            <input type="text" placeholder="Progress" id="ping_progress" value={this.state.progressValue} size="24" readOnly />
            msec
          </form>
        <PingResultError error={this.state.error} />
        </div>
      );
    }
  });
  
  var PingResultError = React.createClass({
    render: function() {
      var error = "";
      if (this.props.error) {
        error = "Problem in sending the result: " + this.props.error + ". Please reload and retry."
      }
      return (
        <div className="pingResultError">{error}</div>
      );
    }
  });
  