Why does the JavaScript generated by tsup use "var" no matter what target is specified in my tsconfig?

[kevincam3]

My target in tsconfig is "target": "ES2022" and "module":"Node16". In these versions of JavaScript and Node both "const" and "let" were available. So I'm trying to understand why the generated JavaScript only uses "var"

[rtritto]

Seems that const and let are only used inside functions.
All const and let at first scope level are replaced with var.
The issue is related to the tree-shaking of esbuild that doesn't work with target (e.g. 'es2020' or 'esnext') option.

Related:

• https://esbuild.github.io/faq/#top-level-var
• const is replaced by var evanw/esbuild#623

PS: as alternative, I'm using pkgroll