CI "JavaScript heap out of memory" (Node / V8)

By Kaveh Alemi·Latchkey

V8 hit its heap ceiling and aborted. In CI this usually happens during a large bundle, type-check, or test run that allocates more than the configured (or default) heap.

What this error means

The process prints FATAL ERROR: ... JavaScript heap out of memory and exits. Raising --max-old-space-size or using a larger runner clears it with no source change.

shell

<--- Last few GCs --->
FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory
 1: 0x... node::Abort()

Common causes

The heap limit is below what the build needs

V8 caps old-space memory; large webpack/tsc/test runs can exceed the default and abort.

A genuine memory blowup

Unbounded in-memory accumulation (huge source maps, leaking watchers) can push usage past any reasonable limit.

How to fix it

Raise the V8 heap

Increase the old-space limit, keeping it below the runner RAM.

shell

export NODE_OPTIONS="--max-old-space-size=4096"
npm run build

Reduce memory pressure or use a larger runner

Disable source maps in CI builds where not needed.
Lower test/build worker concurrency.
Move heavy builds to a runner with more RAM if raising the heap is not enough.

How to prevent it

Set NODE_OPTIONS=--max-old-space-size relative to runner RAM.
Keep CI source-map generation minimal.
Right-size runners for large front-end builds.

Frequently asked questions

What causes "JS heap out of memory"?