The JavaScript heap out of memory error occurs when a Node.js process runs out of memory while attempting to allocate new objects on the heap, resulting in a "FATAL ERROR" message. The heap is a region of memory used by Node.js to store objects created during execution, and once its limit is reached, the process throws an error. This error can be caused by various situations such as processing large amounts of data or running a server with many connections. To fix this error on Linux/MacOS, setting the maximum heap size to 4GB using `node --max-old-space-size=4096` can resolve the issue. On Windows, running the same command in Command Prompt or PowerShell as an administrator can also solve the problem. Additionally, a bug reporting browser extension like Jam can help developers debug faster by creating comprehensive bug reports with auto-included console logs and steps to reproduce the issue.