Is this library pure?

[light0x00]

It's a great project. I love it.
But I see sideEffect is not set in package.json.
so Is this library pure?

[TrySound]

sideEffects: false field does not mean the library is pure. It's mostly a hack for webpack analyzer. Rollup uses it too but it's useful for more complicated cases like transpiled classes. This library is written with only functions.

[kossnocorp]

It's a great project. I love it.

Thank you a lot!

But I see sideEffect is not set in package.json.

It's set in v2 to false in the root directory and each module.

so Is this library pure?

It depends on what you mean by pure. The library code doesn't produce side effects so can be tree-shaken (that's why we have sideEffects). If you mean FP-pure, then yes it doesn't use Date.now at the moment but I'm going to change that, see #1184 but anyways date-fns/fp will stay pure.