Milline on sulgemiste (closures) roll JavaScriptis ja milleks neid kasutatakse?

Closures in JavaScript are functions that "remember" the environment in which they were created, including access to variables from an outer function even after it has finished.

Role of closures:

• Allow creating private variables and methods by encapsulating data.
• Used to create functions with preserved state.
• Help avoid pollution of the global scope.
• Used in functional programming to create functions with partially applied arguments.

Example:

function makeCounter() {
  let count = 0; // private variable
  return function() {
    count += 1;
    return count;
  };
}

const counter = makeCounter();
console.log(counter()); // 1
console.log(counter()); // 2

Here, the inner function retains access to the count variable from the outer function, creating a closure.