Hunting Down Hidden Memory Leaks in JavaScript

Understand What Causes Them and How to Eliminate These Pesky Bugs

``Photo by Bankim Desai on Unsplash

One of the trickiest JavaScript bugs to track down is the dreaded memory leak. Unlike syntax errors or logical bugs, memory leaks don’t crash your code — they just slowly degrade performance over time.

But finding and plugging these leaks is critical for building high-quality JavaScript applications. Let’s break down what memory leaks are, what causes them, and key techniques for detecting and preventing them.

What is a Memory Leak?

In languages with manual memory management like C, a memory leak happens when allocated memory isn’t freed after it is no longer needed. This ties up resources that never get released.

JavaScript uses automatic garbage collection, so manual allocation/freeing isn’t a concern. But memory leaks can still occur when unwanted references to objects or data persist, preventing cleanup.

For example:

function processData() {
  const data = getData(); // large dataset
  addData(data); 
}

If the data variable persists even after the function exits, that large dataset continues occupying memory. These unintended object references are the typical…