All 10 Memory Management & Garbage Collection questions
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How does JavaScript decide when to free memory used by an object? How can an unremoved event listener cause a memory leak? How do closures unintentionally keep large objects alive longer than expected? What is the difference between the generational garbage collection strategy's 'young' and 'old' generations? How does mark-and-sweep garbage collection actually determine which objects are reachable? How can a growing array used as a cache with no eviction policy become a memory leak? How would you use Chrome DevTools' heap snapshot comparison to find a leak's source? Why can setInterval() be a subtle source of memory leaks, and how do you avoid it? How does using WeakMap/WeakSet as a design choice actively prevent certain classes of memory leaks?
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JavaScript › Memory Management & Garbage Collection

What is a memory leak in JavaScript, given that it has automatic garbage collection?

Beginner

Answer

A memory leak happens when objects remain reachable (and therefore never collected) even though the program logically no longer needs them — typically because a lingering reference (a global variable, a forgotten event listener, or a closure) accidentally keeps them alive.
function setup() {
  const bigData = new Array(1000000).fill('x');
  window.leaked = bigData; // accidental global reference keeps it alive forever
}
Real-world example Diagnosing why a single-page app's memory usage keeps climbing the longer a user stays on the page.

Common follow-ups: What browser tool would you use to find the source of a memory leak?

Debugging Testing & Tooling
All 10 Memory Management & Garbage Collection questions