This is probably a must-have interview question, especially for Junior and Middle developers. If you get asked it, your goal is to answer in an unexpected way.
First, explain in simple terms what a closure is.
In simple terms, it is a function's ability to remember the scope in which it was declared.
Let's look at a simple example:
let count = 0;
function createCounter() {
return function () {
// при спробі доступу до count, шукаємо змінну в середині функції
// в середині функції ми її не знаходимо і починаємо шукати вище
// в createCounter змінної теж нема тому ми рухаємось вище
// ми знаходимо count в глобальній області видимості і використовуємо його
count++;
return count;
};
}
const counter = createCounter();
console.log(counter()); // 1
console.log(counter()); // 2
console.log(counter()); // 3
Once you've answered the question, say BUT there is a nuance here.
If you consider closures in the context of high-load or even data-intensive Node.js projects, careless use of them can lead to memory leaks.
This happens because the Garbage Collector does not clean up objects that are still referenced. And if you keep large objects in a closure, you are quite likely to run into memory problems. So it is worth keeping WeakMap, WeakSet, WeakRef in mind.