I haven&#x27;t looked over the changelog&#x2F;breaking changes for 4.0.0, so this may not encompass everything there, but there are a few changes you need to be aware of. How hard it is depends on which functions you use currently, but I doubt it would take more than an hour of find-replace work. They are listed here : <a href="https:&#x2F;&#x2F;github.com&#x2F;lodash&#x2F;lodash&#x2F;wiki&#x2F;Migrating" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;lodash&#x2F;lodash&#x2F;wiki&#x2F;Migrating</a> The ones that affected me the most were the changes to the overloaded _.first, _.last, etc, but YMMV.