Closure

1.What is closures in js?

In JavaScript, a closure is a function that has access to variables in its outer lexical scope, even after the outer function has returned.

To create a closure, you define a function inside another function, and the inner function can access the variables of the outer function, even after the outer function has returned. The inner function forms a closure around the variables of the outer function.

Here's an example:

function outerFunction() {
  let outerVar = "I am in the outer function";
 
  function innerFunction() {
    console.log(outerVar);
  }
 
  return innerFunction;
}
 
let closure = outerFunction();
closure(); // Output: "I am in the outer function"

In this example, outerFunction defines a variable outerVar and a function innerFunction, which logs the value of outerVar to the console. outerFunction then returns innerFunction.

When we call outerFunction, it returns the innerFunction, which we assign to the variable closure. When we call closure, it logs the value of outerVar to the console, even though outerFunction has already returned. This is because closure has formed a closure around the outerVar variable.

Closures are often used in JavaScript to create private variables and methods in object-oriented programming, to implement currying and partial application in functional programming, and to manage asynchronous code.

const firstFn = () => {
  let a = "Im outer function variable";
  function secoundFunction() {
    return a;
  }
  return secoundFunction;
};
 
const fn = firstFn();
console.log(fn()); // Im outer function variable