What is the use of “use strict” in JavaScript?

The “use strict” directive is a way to opt in to a “strict” mode of JavaScript, which is a version of the language that has more stringent rules and restrictions. When “use strict” is included in a JavaScript file or function, it indicates that the code should be executed in strict mode, which provides several benefits, including:

1. Improved error handling: Strict mode provides more informative error messages, making it easier to identify and fix issues in your code.
2. Better security: Strict mode eliminates some of the “unsafe” features of JavaScript, reducing the risk of security vulnerabilities and accidental bugs.
3. Improved performance: Strict mode can result in improved performance, as the JavaScript engine can make certain optimizations that are not possible in non-strict mode.
4. Consistent behavior: Strict mode enforces a more consistent behavior of the language, making it easier to write and maintain your code.

To use “use strict”, you simply include the directive at the top of your JavaScript file or function:

"use strict";

// Your code here...

It’s important to note that “use strict” only applies to the scope in which it is declared. If you declare “use strict” in a function, it will only affect the code inside that function. To enforce strict mode for an entire file, you must include the directive at the top of the file, outside of any functions.

In general, it’s a good practice to use “use strict” in your JavaScript code, as it can help you write safer, more secure, and more performant code. However, be aware that strict mode can also introduce breaking changes to your code, so be sure to thoroughly test your code after adding “use strict”.