version 3.1.3 bumped to lru-cache@5.1.1 which is not es5 compatible https://github.com/kuitos/axios-extensions/commit/2b63345e52e5d0c33e1a0705c947c3cd56f5cbcb It might even be that lru-cache is purely meant for node: https://github.com/kuitos/axios-extensions/commit/2b63345e52e5d0c33e1a0705c947c3cd56f5cbcb If that’s the case, I propose locking an older version of lru-cache until something more future-proof is done in this regard. I can push a PR, temporarily locking in the most recent version of lru-cache that worked as expected in ES5 environments.