What does un-shimmable mean?

Question

I read through the vuejs2 documentation and found this part:

This is an ES5-only and un-shimmable feature, which is why Vue doesn’t support IE8 and below.

I think it means that the feature is not possible to be monkey patched, but I'm not sure.

So what is a (un-)shimmable feature in JavaScript exactly all about?

Answer 1

You got it right, a shim is a patch that provides otherwise unavailable functionality or a language feature.

Some features, however, require support from the underlying JS engine, and cannot be created purely in Javascript. I imagine that's what they meant.