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Try adding "type": "module" to your package.json.

Better to use as following:

You need the default of it you can destructure the default property like this:

fs.writeFileSync doesn't write file in UTF-8

Actually it did. US-ASCII is a subset of UTF-8 for characters with a character code 127 and below. So, it's both US-ASCII and UTF-8.

For plain ascii characters below 127, there is no physical difference between UTF-8 and US-ASCII. US-ASCII characters encode to themselves in UTF-8.

A file like you're writing doesn't typically record what character set it is. It's up to the reading software to either infer the encoding from the data it finds or use other clues such as the file extension to guess. So, your program is just telling you that your file meets all the requirements of US-ASCII and thus looks like US-ASCII which happens to be a subset of UTF-8.

Put some Japanese characters in there and it will look different since they don't fit into US-ASCII. They will use multiple bytes to encode properly.