rewrite top-level this as undefined - #707

Looks good.

To bundle the code for non-Node environments, sometimes this is needed on top-level. For someone like me, this is a simple workaround for it, kind of:

doSomething(that)

Add intro option:

const code = bundle.generate({
  intro: 'const that = this'
}).code;

Then the output:

const that = this
doSomething(that)

For anyone else landing here -> #858

Cool!