What are core files by node.js

core.<number> files are typically memory dumps created on Linux systems. The <number> is the Process ID of the process that crashed.

I guess your Node.JS application has crashed a number of times and these are the memory dumps left there for you to debug.

Yea that's not normal if they are in your project file. To all the people that are downvoting his question, it's a question perfectly worth asking especially if it's in the app folder.

fefe: Can you see any sub dir within the core dir?

those look like memory dumps. So I guess you should be fine to delete them unless you want to go through them for debugging purposes.

Give this a try for debugging those crashes: https://github.com/ddopson/node-segfault-handler