Man this library is really tempting.

absolutely! currently using Insomnia which is based on it..

What do you use for transaction building? BITBOX is nice, but very heavy (something like 1mb)

this library is currently server-side only (until websocket support is avail), so why would 1mb matter?? regardless, BITBOX is too unstable for production anyway, I'd recommend Bitcore Lib Cash by BitPay..

I used to use a mix of bitbox and bitcore-lib-cash, both heavy and bloated, but not too long ago libauth was released and while it's early still, it is based on webassembly, functional programming and it has 0 dependencies: https://www.npmjs.com/package/@bitauth/libauth

It's made by jason who I believe is a former employee at bitpay, and the code has its root in bitcore-lib - I can't be 100% sure that it's going to turn out to be the greatest thing since sliced bread, but that 0-dependency part is really attractice.

However, it's not small in filesize, since it contains all the parts that would normally come from dependencies, so not sure if it'd be viable for web-use, unless the tree-shaking / dead-code-elimination part works out really well.