Definitely was able to get a repro on this, pretty bizarre. I actually get an error from smoke error saying that String doesn't have a toString symbol, so it seems like it thinks that runtimeType is a String for some reason?

Set owner to @jakemac53.
Removed Priority-Unassigned label.
Added Priority-Medium label.

Added Started label.

turns out "String" here is because that's the string representation of the String type.

The error seems to be that smoke assumes that

  smoke.invoke(A, #foo)

is a static method call. Turns out that no, in this case it is an instance method.

Fixed in r40469 and released a new smoke version 0.2.1+1

Removed Pkg-Polymer label.
Added Pkg-Smoke, Fixed labels.

Note that with dart2js minification there is no guarantee that model.runtimeType.toString() will be 'Foo', it might be mangled.

It might be better for your code to expose the expressions you need in a different way. For example:

if="{{mode.runtimeType == fooType}}"

Where fooType is a getter in your custom-element that returns Foo.

You could also do the updates in 2 steps (this however means that the UI will require 2 rounds of observable notifications, rather than 1:

@observable
bool isFoo;

@ObserveProperty('model')
updateIsFoo() {
  isFoo = model.runtimeType == Foo;
}

Cheers,
Siggi

This issue has been moved to dart-archive/smoke#17.