🧠 Memory Leaks in JavaScript — a production issue I caused myself A while ago, I was debugging a frontend issue where: ✅ The UI worked correctly ✅ There were no errors ❌ The application became slower over time After digging deeper, I realized the problem wasn’t the API or React re-renders. I hadn’t cleaned up properly. Event listeners and timers were still alive even after components were gone. That’s when I went down the rabbit hole of JavaScript memory leaks. Here are the key patterns I learned (and now actively watch for): 🔴 1. Accidental Global Variables A small mistake that can silently leak memory. function createLeak() { leakedData = new Array(10000).fill("*"); // becomes global ❌ } Correct fix: "use strict"; function createLeak() { const data = new Array(10000).fill("*"); // properly scoped ✅ } 🔴 2. Event Listeners Without Cleanup (my main issue) Removing a DOM element does not remove its event listeners. button.addEventListener("click", () => { console.log("clicked"); }); // button removed, listener still retained ❌ Correct fix: function handleClick() { console.log("clicked"); } button.addEventListener("click", handleClick); // cleanup button.removeEventListener("click", handleClick); 🔴 3. Closures Holding Unnecessary Data Closures keep references alive longer than expected. function createHandler() { const largeData = new Array(10000).fill(1); return () => console.log(largeData.length); } const handler = createHandler(); // largeData stays in memory ❌ Better approach: Avoid capturing large or long-lived data inside closures unless required. 🔴 4. Timers That Never Stop Timers are another common source of leaks when not cleaned up. setInterval(() => { console.log("running..."); }, 1000); Correct fix: const id = setInterval(() => { console.log("running..."); }, 1000); clearInterval(id); 🧪 What this experience taught me Garbage collection isn’t a safety net for poor cleanup Memory leaks rarely fail fast — they degrade performance over time Long-running SPAs are especially vulnerable Since then, I make it a habit to: ✅ Clean up event listeners and timers ✅ Review closures carefully ✅ Treat useEffect cleanup as mandatory, not optional 🚀 Final thought Most memory leaks don’t break applications — they quietly erode performance. And very often, the root cause isn’t complex logic — it’s missing cleanup. 💬 Curious: Have you ever debugged a memory leak in production? What turned out to be the root cause? #JavaScript #FrontendEngineering #WebPerformance #React #LearningInPublic #SoftwareEngineering
great read Kushagra!
Penned it down accurately