How to fix “fatal reached heap limit allocation failed javascript heap out of memory”

This content originally appeared on DEV Community and was authored by Abdiel Wilson

How to Fix "JavaScript Heap Out of Memory" Error in Node.js

If you've ever encountered the dreaded "JavaScript heap out of memory" error while working with Node.js, you're not alone. This error occurs when Node.js runs out of memory, typically during large builds or memory-intensive processes. In this post, I'll explain why this error happens and walk you through a few solutions to resolve it.

Why Does This Error Occur?

Node.js, like many JavaScript runtimes, has a default memory limit for the heap (the area where memory is allocated for objects and variables). For many processes, this default limit is sufficient, but when dealing with larger applications, especially during build steps with tools like Webpack or Vite, the allocated memory might not be enough.

When Node.js runs out of memory, it throws the "JavaScript heap out of memory" error. The solution? Increase the memory Node.js can use, or optimize your code to use memory more efficiently. Below are a few ways to tackle this issue.

Solution 1: Increase Node.js Memory Allocation

One of the quickest and easiest fixes for this issue is to increase the memory Node.js allocates for its processes. You can do this by adding the --max-old-space-size flag when running your script.

For example, let’s say you want to allocate 4GB of memory:



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

If you're running a script via npm (e.g., an npm build command), you can prepend this command:



node --max-old-space-size=4096 node_modules/.bin/vue-cli-service build

Pro tip: The number 4096 represents memory in MB, so adjust this value according to your needs.

Solution 2: Set Environment Variable to Automatically Increase Memory

Instead of modifying individual commands every time, you can also set an environment variable to globally increase memory for all Node.js processes. This ensures the new memory limit is applied automatically.

On Linux or macOS:



export NODE_OPTIONS="--max-old-space-size=4096"

On Windows (Command Prompt):



set NODE_OPTIONS=--max-old-space-size=4096

On Windows (PowerShell):



$env:NODE_OPTIONS="--max-old-space-size=4096"

Once this variable is set, you can run your usual Node.js commands, and they'll have increased memory allocation.

Solution 3: Optimize Code and Build Process

While increasing the memory limit is an effective quick fix, it’s a good idea to investigate the root cause, especially for larger applications. Here are a few tips to optimize your code and the build process:

Look for Memory Leaks: Ensure your code doesn't contain memory leaks that unnecessarily consume memory over time.
Break Down Larger Tasks: If you're performing large operations in one go, try breaking them into smaller, more manageable tasks.
Use Production Optimizations: If you're running in a development environment, enabling production optimizations can help reduce memory usage. Tools like Webpack, Vite, and Rollup have specific production configurations that minimize the resources needed.

For instance, in Webpack, make sure to set the mode to production to optimize memory usage.

Conclusion

The "JavaScript heap out of memory" error can be a major headache, but increasing Node.js memory allocation or optimizing your build process can resolve the issue. Start by increasing the memory limit using the --max-old-space-size flag, and if the problem persists, look for optimizations in your codebase.

By taking these steps, you can ensure that your Node.js application continues running smoothly, even for the largest projects.

Have you encountered this error before? Share your experience and solutions in the comments below!