Everyone likes to bring up this same issue each time which is rarely an issue in practice. Yes, numeric overflows have different behavior because of Dart's variable integers vs JS where all numbers are floats behind the scenes.
There is a VM and command-line `throw_on_javascript_int_overflow` flag that can be used to throw an error if there is any such overflow in your app.
Ideally when BigNums lands in JS this will no longer be an issue.
Things that rarely happen in practice aren't mine-fields. The only common thing in this issue is that it's brought up in every Dart thread, the actual issue of integer overflows is itself rare and usually an indication of a bug in your program.
[0] https://code.google.com/p/dart/issues/detail?id=1533