What is "use strict" in JavaScript, and how does it help prevent common mistakes?

What is "use strict" in JavaScript?

"use strict" is a special statement that makes JavaScript run in strict mode.
Strict mode makes JavaScript:

• More safe
• More careful
• More error-friendly

Why Do We Use It?

Because normal JavaScript sometimes allows mistakes silently.
Strict mode:

• Stops undeclared variables
• Prevents duplicate parameter names
• Catches common bugs early

Simple Example

❌ Without "use strict"

x = 10;
console.log(x);

This works.

But wait…
We never declared x using let, var, or const.
JavaScript silently creates a global variable.
That can cause problems later.

✅ With "use strict"

"use strict";
x = 10;

Now JavaScript gives an error.
Because x was not declared.

One-line Summary
"use strict" helps prevent common mistakes by making JavaScript stricter.