If ESLint is running in the terminal but not inside VSCode, it is probably
because the extension is unable to detect both the local and the global
node_modules folders.
To verify, press Ctrl+Shift+U in VSCode to open
the Output panel after opening a JavaScript file with a known eslint issue.
If it shows Failed to load the ESLint library for the document {documentName}.js -or- if the Problems tab shows an error or a warning that
refers to eslint, then VSCode is having a problem trying to detect the path.
If yes, then set it manually by configuring the eslint.nodePath in the VSCode
settings (settings.json). Give it the full path (for example, like
"eslint.nodePath": "C:\\Program Files\\nodejs") — using environment variables
is currently not supported.
This option has been documented at the ESLint extension page.