🧵 What Is a Closure in JavaScript (And Why It Matters)?

Closures are one of the most asked-about — and misunderstood — concepts in JavaScript interviews.

Let’s simplify it.

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🔍 What’s a Closure?

A closure happens when a function "remembers" the variables from its lexical scope, even after that outer function has finished running.

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🧪 Example:

jsCopyEditfunction outer() {
  let count = 0;

  return function inner() {
    count++;
    console.log(count);
  };
}

const counter = outer();

counter(); // 1
counter(); // 2
counter(); // 3

Even though outer() is done running, the inner() function remembers the variable count.

That’s a closure!

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🧠 Why Are Closures Useful?

• ✅ Data privacy (like private variables)

• ✅ Building factories and utilities

• ✅ Avoiding global variables

• ✅ Powering functions like setTimeout, event handlers, and more

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🎯 Real-World Use

jsCopyEditfunction createLogger(prefix) {
  return function(message) {
    console.log(`[${prefix}] ${message}`);
  };
}

const errorLog = createLogger("ERROR");
errorLog("Something went wrong"); // [ERROR] Something went wrong

Closures make this possible!

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🔑 Key Takeaway

A closure is when a function "closes over" the variables from its surrounding scope — and keeps access to them even after the outer function is gone.

Mastering closures = leveling up your JavaScript skills 🔥