What is the difference between strict mode and non-strict mode in JavaScript?

What is the difference between strict mode and non-strict mode in JavaScript?

Strict mode is a way to opt in to a restricted variant of JavaScript, which helps catch common coding errors and unsafe actions.

Can you give me examples of what strict mode prevents?

Sure! For instance, in strict mode, you can't use undeclared variables, and assignments to read-only properties will throw an error.

Is strict mode enabled by default in JavaScript?

No, strict mode is not enabled by default. You have to explicitly enable it by adding 'use strict'; at the beginning of your script or function.

Are there any performance differences between the two modes?

Generally, strict mode can lead to better performance optimizations by the JavaScript engine, but the difference is often minimal.