Understanding Closures in JavaScript (With Real Examples)

Closures confuse a lot of developers at first. But once you understand them, they unlock powerful patterns.

🧠 What is a closure?

A closure happens when a function “remembers” variables from the scope where it was created — even after that scope has finished.

Example: Counter Function

function createCounter() {
  let count = 0;
  return function() {
    count++;
    return count;
  };
}

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

The inner function keeps access to count, even though createCounter has returned.

Why Closures Are Useful

• Encapsulation (hide private state).
• Factories (generate functions with pre-filled values).
• Event handlers and async callbacks.

🚀 Key Takeaways

• Closures = function + environment.
• They make JS flexible but can also cause memory leaks if misused.
• Learn them once, and you’ll see them everywhere (React hooks, Node APIs, etc).