@KeverJul 15.2017 — #I rarely use it. You can read https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode and decide for yourself when to use it. It can help if you need to write performant scripts for like a game. Just keep in mind that it only works from IE10+. Older browsers will run that script in standard mode, and will might behave unexpected.