<StrictMode /> is a component included with React to provide additional visibility of potential issues in components. 

If the application is running in development mode, any arising issue is logged to the development console, but these warnings are not shown if the application is running in production mode. 

Developers use to find problems such as deprecated lifecycle methods and legacy patterns, to ensure that all React components follow current best practices. 

can be applied at any level of an application component hierarchy, which allows it to be adopted incrementally within a codebase.

 

The docs for are added below Strict Mode enables the following development-only behaviors: Your components will re-render an extra time to find bugs caused by impure rendering. 

Your components will re-run Effects an extra time to find bugs caused by missing Effect cleanup. Your components will re-run refs callbacks an extra time to find bugs caused by missing ref cleanup. Your components will be checked for usage of deprecated APIs.