fix(esbuild): object sourcemap by overriding Object.prototype.toString

[edemaine]

Currently, if you:

• use esbuild mode of an unplugin, and
• return a map from a load handler, where the map is produced by JSON.parseing a JSON sourcemap (e.g. as returned by esbuild itself),

then unplugin ends up outputting a sourcemap of [object Object] (encoded in base64) because it overrides toUrl but not toString that's inherited from the Object prototype.

I believe the simple fix in this PR (use Object.hasOwn instead of in, to avoid checking prototypes) is what is intended, and it fixed the bug I was encountering.

Full (but not small) reproduction: https://github.com/DanielXMoore/Civet/tree/main/integration/unplugin-examples/esbuild with sourceMap: true added to options in esbuild.js, and v0.7.22 of @danielx/civet (I'm about to release a workaround).

[pkg-pr-new]

commit: 505e6fa

pnpm add https://pkg.pr.new/unjs/unplugin@399

Open in Stackblitz