Running dart code in dartium

[Test This]

Just started using Dart and so far I am enjoying it. Overall, it feels great. 

However, I have run into a problem. Overall, I need some advice about a more efficient workflow, but here is my specific problem. 

Right now I write dart code, compile it to js using dart2js and then refresh the page to see if things are working as expected. With this, the problem is that when there is an error, I have no idea what it is. For example, I made a silly error where I defined 

and then tried adding cell elements to tr (instead of doing