Psbt addOutput mutates the target

[landabaso]

It's really a minor thing.

addOutput adds the script property to the target (mutating it) here:

bitcoinjs-lib/src/psbt.js

Line 238 in 59b2116

outputData = Object.assign(outputData, { script });

As I said it's just a minor thing that I noticed because my tests were failing since I was comparing target objects to final tx retrieved from regtest chain and was not expecting this object to had been changed.

Could be easily solved with something like this:

outputData = {...outputData, script}; 

As a workaround I'm cloning the input parameter so it's not a big deal but might be nice to correct it in future releases.