What defines a 'closure' in JavaScript?

• A. A function that uses global variables
• B. A function that retains access to its lexical scope
• C. A function that cannot be executed outside its declaration
• D. A function that is executed repeatedly

Answer: (B)

A closure in JavaScript is defined as a function that retains access to its lexical scope even when the function is executed outside that scope. When a function is created, it creates a new scope, and any variables defined within that scope are preserved as long as the function retains a reference to its environment. This means if you define a function inside another function, the inner function can still access variables from the outer function, even after the outer function has finished executing.

This characteristic of closures allows for powerful programming patterns, such as encapsulation, data hiding, and maintaining state across function calls, which can lead to more modular and manageable code. For instance, a closure can be created to keep track of a variable without exposing it to the global scope, offering a way to maintain private data.