[philbo]

This attitude really surprises me. I've been deploying 'use strict' code to live environments since 2012 and genuinely can't recall a single occasion where it has caused us a problem.

We lint, unit-test and acceptance-test aggressively (including legacy browsers), and the strict directive itself is of course scoped to our own IIFE. Perhaps that explains why I've not witnessed the hurt you mention.

The mechanics of strict mode are very clearly defined too, so I've not seen any cases were developer confusion caused unwanted side-effect (although I have heard straw-man arguments made where people predict it would).

The benefits, on the other hand, are real and tangible. Errors that might otherwise be difficult to diagnose fail hard and obviously. Browsers are better able to optimise strict code than non-strict. And culturally, I suspect that a use-strict policy has forced everyone to be more clinical in their approach.

Hand on heart, I would never go back to deploying non-strict code, so would be really interested to hear from anyone else in the opposite camp.