The Popups extension has maxWarnings: 0 in Gruntfile.js (I am not sure if that is the only wait to set it)
In this case Libup has to set also the warnings (along with errors) in .eslintrc.json to off,
Running "eslint:all" (eslint) task /src/repo/src/preview/model.js 9:0 warning Invalid JSDoc tag (preference). Replace "const" JSDoc tag with "constant" jsdoc/check-tag-names 36:0 warning @extends should not have a bracketed type in "typescript" mode jsdoc/valid-types 51:0 warning @extends should not have a bracketed type in "typescript" mode jsdoc/valid-types ✖ 3 problems (0 errors, 3 warnings) 0 errors and 1 warning potentially fixable with the `--fix` option. Warning: ESLint found too many warnings (maximum: 0) Use --force to continue.