Yes, sorry, thin arrow, not single - `() -> this.foo()` for function expressions and possibly even `let/const fn () -> this.foo()` for declarations.

Excuse my ignorance but I only have experience in JS and not any other "advanced" or well-established programming langs, how's thin arrow syntax gonna fix this prob that fat arrow can't?

Fat arrow functions have lexical this: this inside the function is bound to what it was outside. Thin arrow functions have a dynamic this, determined by how they are called. Because the library relies on dynamic this as the place where the data is sent, fat arrow syntax isn't useful with it.

Thanks for the explanation.