What are Closures in JavaScript?

A closure is a function that has access to its own scope, as well as the scope in which it was defined. This means that a function can access variables from its parent function even after the parent function has finished executing.

Uses of Closures

1. Data privacy: Closures can be used to create private variables in JavaScript, as the variables are only accessible within the closure.
2. Function factories: Closures can also be used to create functions with pre-defined configurations or states.
3. Callback functions: Closures are commonly used with callback functions to maintain context and state.

Example of Closures

function outerFunction() {
  let outerVar = 'I am the outer variable';

  function innerFunction() {
    console.log(outerVar);
  }

  return innerFunction;
}

const closure = outerFunction();
closure(); // Output: I am the outer variable

Interview Questions on Closures

1. What is a closure and how is it created in JavaScript?
2. Why are closures useful in JavaScript programming?
3. How does a closure maintain access to outer variables even after the outer function has finished executing?
4. Can you provide an example of using closures to create private variables in JavaScript?
5. Explain the concept of function factories using closures.

In conclusion, closures are a powerful and versatile feature in JavaScript that can be used for various purposes such as data privacy, creating reusable functions, and maintaining context in callback functions.