How to Diagnose and Fix JavaScript Memory Leaks in Node.js Applications

Memory leaks in Node.js often manifest as containers running smoothly for roughly 40 minutes before the heap grows steadily, garbage collection intensifies, latency spikes, and the process is killed with OOMKilled. A common misconception is that JavaScript's garbage collector uses reference counting; in reality, V8 uses a mark-and-sweep algorithm that collects any object unreachable from GC roots, making isolated circular references harmless. The V8 heap is generational, and true leaks occur when objects are promoted to old space and never freed, which can be confirmed by monitoring heap size after forced major GC cycles using the --expose-gc flag. If heap usage rises monotonically across multiple samples under steady load, a JavaScript heap leak is confirmed; a stable heap with rising RSS instead points to leaks in native buffers or allocator fragmentation. One of the most frequent causes of leaks in both Node.js and single-page applications is unremoved event listeners, which create strong references from emitters to handlers and everything captured in their scope.