この記事はまだボランティアによって 日本語 に翻訳されていません。ぜひ MDN に参加して翻訳を手伝ってください！
ECMAScript 5 and later let scripts opt in to a new strict mode, which alters the semantics of JavaScript in several ways to improve its resiliency and which make it easier to understand what's going on when there are problems.
The normal, non-strict mode of JavaScript is sometimes referred to as sloppy mode. This isn't an official designation, but you are likely to come across it if you spend time doing serious JavaScript code.
Learn more
General knowledge
- "Strict Mode" in chapter 7 ("JavaScript Syntax") in the book Speaking JavaScript.