JS Tutorial

JavaScript Strict Mode 🔐

Strict Mode is a way to opt in to a restricted variant of JavaScript. It helps you write cleaner code and catch common bugs earlier.

🔧 Enabling Strict Mode

To enable strict mode, add "use strict"; at the beginning of a script or a function:

"use strict";
x = 10; // ❌ Error: x is not defined

Without strict mode, this would not throw an error:

x = 10; // ✅ Allowed in non-strict mode (but bad practice)

📋 Benefits of Strict Mode

• Prevents usage of undeclared variables
• Makes assignments to read-only properties throw errors
• Disallows duplicate parameter names
• Helps avoid using reserved keywords

💡 Example in Function Scope

function demo() {
  "use strict";
  let y = 20;
  // z = 30; // ❌ Error: z is not defined
}

🧪 Try It Yourself