What are some advanced examples of JavaScript strict mode?

Can you explain what JavaScript strict mode is?

Sure! JavaScript strict mode is a way to opt in to a restricted variant of JavaScript, which helps catch common coding errors and 'unsafe' actions such as defining global variables.

What are some advanced examples of using strict mode?

Here are a few advanced examples: 1) Preventing the use of undeclared variables, 2) Disallowing duplicate parameter names, and 3) Making 'this' undefined in functions.

Can you show me a code snippet for preventing undeclared variables?

Certainly! Here's a simple example:

'use strict';

function myFunction() {
    x = 3.14; // This will throw an error because x is not declared
}
myFunction();

What happens if I try to use duplicate parameter names?

In strict mode, using duplicate parameter names will throw a SyntaxError. For example:

function myFunction(a, a) { // SyntaxError
    return a;
}