How to get unspents for inputs using bitcoinjs-lib?

I would like my simple wallet app to automatically select UTXOs for inputs. I realize that I can’t accomplish this with just bitcoinjs, but is there something I can add to it to keep track of unspents? Or is there a way to use some sort of API to automatically select unspents? I do see that it is fairly easily done with BTC.com, but I would like to be able to do this with altcoins as well. Thanks in advance!