Fatal error: how to fix Javascript heap out of memory error

Sometimes when a Node.js process runs out of memory while attempting to allocate new objects on the heap you'll into a "FATAL ERROR" message with the details being "Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory".

What is the heap in Node.js and Javascript?

The heap is a region of memory that is used by Node.js in order to store objects created during the execution of a program. When this memory is full, Node.js attempts to allocate more memory, up to a certain limit.

Once that limit is reached and there is still not enough memory available, the process will throw a "FATAL ERROR" message instead.

The error get thrown in a variety of situations, to enumerate a few:

1. When attempting to process large amounts of data or execute complex algorithms that require a lot of memory.
2. When running a Node.js server with a large number of connections or concurrent requests.
3. When running a Node.js application in a container or virtual machine with limited memory resources.

How to fix JavaScript heap out of memory

Linux/MacOS

To fix the error on either Linux or MacOS, you can run the below code to set the maximum heap size to 4GB.

node --max-old-space-size=4096 server.js

Alternatively, if you're using a Docker container to run your Node.js, use this code:

docker run -m 4g myapp

Windows

To fix the same error on Windows installation, follow these steps:

1. Open Command Prompt or PowerShell as an administrator.
2. Navigate to your Node.js application directory using the "cd" command.
3. Run the following command to start your Node.js application with a larger memory limit:

node --max-old-space-size=4096 server.js

Conclusion

Using the above commands you'll be able to fix the JavaScript heap out of memory error on both Linux based operating systems and Windows.