WARNING: jsvGetString Overflowed

It's a bug - I'll file an issue for it. The length of IDs in Espruino is limited - but that should only be for things like function names.

The problem is when Espruino tries to check all of the built-in methods as well.

For now, I'd recommend that you just use in:

function foo() {
  var bar= {"acbdefghijklmnopqrstuvwxyz1234567890":2};
  console.log(bar, "acbdefghijklmnopqrstuvwxyz1234567890" in bar);             
}