add index output to rollup config

[adamjanicki2]

Currently, to import Treecle via ESM, after npm installing, you have to write

import Treecle from "treecle/dist/treecle.js"

but it would be nice if you could just do

import Treecle from "treecle"

so this fix just adds an index.js to the output dist directory so that you can do that

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[LeaVerou]

We don't need an index.js for this, just certain package.json fields (main, exports, not sure if there are others that are relevant).

[adamjanicki2]

We don't need an index.js for this, just certain package.json fields (main, exports, not sure if there are others that are relevant).

Got it, currently the relevant fields are set to

"main": "./dist/treecle.cjs",
"module": "./dist/treecle.js",

I think the issue is the build is outputting a file called treecle.cjs.js, so the target for main is off. Is the correct fix to change the package to "main": "./dist/treecle.cjs.js", or to adjust the rollup config so that it names the file treecle.cjs?