JavaScript use strict

"use strict" in JavaScript enables strict mode which makes the code more secure, optimized, and easier to debug by enforcing stricter parsing and error checks.

Why Use "use strict"?

• Prevents use of undeclared variables.
• Disallows duplicate parameter names.
• Throws errors on silent failures.
• Disables problematic or deprecated features.
• Ensures better compatibility with future JavaScript versions.

How to Use Strict Mode

1. At the Top of a Script

2. Inside a Function

Differences Between Strict and Non-Strict Mode

Examples

Example 1: Undeclared Variable

Example 2: Duplicate Parameters

Example 3: this in a Function

Example 4: Writing to Read-Only Property

Key Takeaways

• "use strict" enforces stricter rules and better error detection.
• Helps prevent common bugs by catching silent errors.
• Can be applied globally or locally within functions.
• Recommended for writing cleaner, safer, and future-proof JavaScript code.
• Changes behavior of variables and functions to be more consistent.