Javascript: What is eslintcache file and why is always generated in create react app

eslint goes over your code and reports stylistic errors. Usually going over the whole code is unneccessary, because you only changed a few files since the last run. To be able to track which files changed, and which errors occured in the files which were not changed, eslint is writing a cache (into the file you found).

Usually that file is supposed to be in /node_modules/.cache/, so you usually won't notice it. That it resides in your working directory is a bug.