"Cannot redeclare block-scoped variable length"

[JacksonKearl]

When I try to work on a JS file that has a "const length = 100" line at the top with "js/ts.implicitProjectConfig.checkJs": true, I get an ugly "Cannot redeclare block-scoped variable length" error because it conflicts with some lib.dom.ts file... but that's in fact not a concern at all:

I think something like this would probably pose a significant barrier to folks trying to get started with checkJS.

[mjbvz]

This is a duplicate of #31783

Moving upstream for more feedback. I don't think the code causes issues when run in a browser

[JacksonKearl]

Correct, I tried in node and browser contexts with no issues.

[RyanCavanaugh]

The problem here is that if you downlevel this code to var, it starts misbehaving again, and we don't know whether or not you're doing that. Beside that, we could add some logic here to separate the "global scope that's actually global" and the "global scope that is shadowable with a block-scope let/const" but to be honest this really doesn't seem to come up much.