Regression: exception when compiling a = {[-1]: 1}

[StephanHoyer]

Worked in v0.17.19.
Does not work in 0.18.3

I fixed it in userland by converting it to a string first (which is done anyways by JS)

[hyrious]

This issue is saying --minify incorrectly removes the [] from [-1] from 0.18.0, which leads to a syntax error (a = { -1: 1 }). playground link

[StephanHoyer]

that was fast.... thanks @evanw

And thanks for your awesome work in this wonderful piece of software!