39. Memory management and leaks

V8 automatically reclaims memory no longer reachable from any root reference (globals, the call stack, closures). A memory leak in JavaScript means objects that should be garbage are still reachable — commonly through a growing array/Map that's never cleared, forgotten event listeners, or closures capturing more than intended.

js
// leak: this array grows forever, and the listener is never removed
const cache = [];
emitter.on("data", (chunk) => cache.push(chunk));

// fix: bound growth and remove listeners when done
const cache2 = [];
const MAX = 1000;
function onData(chunk) {
  cache2.push(chunk);
  if (cache2.length > MAX) cache2.shift();
}
emitter.on("data", onData);
// later: emitter.off("data", onData);

`node --inspect` plus Chrome DevTools' heap snapshot tool is the standard way to diagnose a real leak: take two snapshots under load, minutes apart, and compare which object types grew unexpectedly.

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