Strict mode - MDN Web Docs Glossary: Definitions of Web-related terms 编辑

JavaScript's strict mode is a way to opt in to a restricted variant of JavaScript, thereby implicitly opting-out of "sloppy mode". Strict mode isn't just a subset: it intentionally has different semantics from normal code.

Strict mode for an entire script is invoked by including the statement "use strict"; before any other statements.