What is a JavaScript Heap Out of Memory?

This fatal error crashes the Node.js process when the V8 JavaScript heap is exhausted. Unlike most errors, it cannot be caught with try/catch because it is a hard process abort. The default heap size is roughly 1.5 GB on 64-bit systems.

Why it happens

• •Accumulating large amounts of data in memory instead of streaming.
• •A memory leak from closures, event listeners, or global caches that grow unboundedly.
• •Loading an entire large file or database result set into memory at once.
• •The heap size is insufficient for the workload and needs to be increased.

Examples

const data = [];
while (true) {
  data.push(new Array(10000).fill("x"));
}

FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory
 1: 0xb7c2e0 node::Abort() [node]
...
Aborted (core dumped)

// Increase heap size as a short-term fix
// node --max-old-space-size=4096 app.js

// Long-term: process data in streams instead
const { Readable } = require("stream");
const readable = Readable.from(generateData());
readable.on("data", (chunk) => process(chunk));

Related errors

• MemoryError
• MaxListenersExceededWarning
• Event Listener Memory Leak