This is what I've used. I don't know about efficiency here, but it's a good and well provisioned library
— /math 9007199254740991 + 2
— 9007199254740992
— Mathjs uses JS numbers
— So that won't help
— Does this use mathjs?
— Yep
— But try it on your own with the lib
— Probably an old version
— I would create codepen to test js libs there, it should operate on strings not numbers.. mathjs doesnt have online calculator probably it's not the best tool around