lint: ignore js file

[jannyHou]

Fixes #4205

Checklist

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• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated
• Documentation in /docs/site was updated
• Affected artifact templates in packages/cli were updated
• Affected example projects in examples/* were updated

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[jannyHou]

The ts eslint rules like @typescript-eslint/prefer-nullish-coalescing shouldn't check js file

[raymondfeng]

Is it required for the build to pass? We already have this override - https://github.com/strongloop/loopback-next/blob/master/packages/eslint-config/eslintrc.js#L158

[jannyHou]

@raymondfeng Not really, our code base is good, and adding this line results in lint error...
But the todo example created by lb4 example complains:

lb4 example (choose todo)
cd loopback4-example-todo
npm i
npm run lint

> @loopback/example-todo@1.9.4 lint /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> npm run prettier:check && npm run eslint
> @loopback/example-todo@1.9.4 prettier:check /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> npm run prettier:cli -- -l
> @loopback/example-todo@1.9.4 prettier:cli /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> lb-prettier "**/*.ts" "-l"
> @loopback/example-todo@1.9.4 eslint /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> lb-eslint --report-unused-disable-directives .
/Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo/index.js
  15:30  error  Prefer using nullish coalescing operator (`??`) instead of a logical or (`||`), as it is a safer operator  @typescript-eslint/prefer-nullish-coalescing

✖ 1 problem (1 error, 0 warnings)
  1 error and 0 warnings potentially fixable with the `--fix` option.

[raymondfeng]

I see. I wonder why https://github.com/strongloop/loopback-next/blob/master/packages/eslint-config/eslintrc.js#L158 does not exclude js files. Can you check which version of @loopback/eslint-config is pulled in?

[jannyHou]

@raymondfeng It's already on the latest released version @loopback/eslint-config@5.0.1

[raymondfeng]

Maybe add a file similar as https://github.com/strongloop/loopback4-example-shopping/blob/d0f6d7543c1a861dc4a4281b6ef7b8ac8d1085dc/.eslintrc.js?

[jannyHou]

@raymondfeng 👍 tested the config file, I think the necessary config is extends: ['@loopback/eslint-config']

Details verified in comment #4431 (comment)

[jannyHou]

Verified with the latest cloned todo example:

before adding the .eslintrc.js file
jannyHous-MacBook-Pro:loopback4-example-todo jannyhou$ npm run lint

> @loopback/example-todo@1.9.4 lint /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> npm run prettier:check && npm run eslint


> @loopback/example-todo@1.9.4 prettier:check /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> npm run prettier:cli -- -l


> @loopback/example-todo@1.9.4 prettier:cli /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> lb-prettier "**/*.ts" "-l"


> @loopback/example-todo@1.9.4 eslint /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> lb-eslint --report-unused-disable-directives .


/Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo/index.js
  15:30  error  Prefer using nullish coalescing operator (`??`) instead of a logical or (`||`), as it is a safer operator  @typescript-eslint/prefer-nullish-coalescing

✖ 1 problem (1 error, 0 warnings)
  1 error and 0 warnings potentially fixable with the `--fix` option.

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @loopback/example-todo@1.9.4 eslint: `lb-eslint --report-unused-disable-directives .`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @loopback/example-todo@1.9.4 eslint script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/jannyhou/.strong-registry/official.cache/_logs/2020-01-14T21_08_58_677Z-debug.log
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @loopback/example-todo@1.9.4 lint: `npm run prettier:check && npm run eslint`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @loopback/example-todo@1.9.4 lint script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/jannyhou/.strong-registry/official.cache/_logs/2020-01-14T21_08_58_705Z-debug.log

jannyHous-MacBook-Pro:loopback4-example-todo jannyhou$ npm run clean

> @loopback/example-todo@1.9.4 clean /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> lb-clean *example-todo*.tgz dist tsconfig.build.tsbuildinfo package

after adding the .eslintrc.js file
jannyHous-MacBook-Pro:loopback4-example-todo jannyhou$ npm run lint

> @loopback/example-todo@1.9.4 lint /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> npm run prettier:check && npm run eslint


> @loopback/example-todo@1.9.4 prettier:check /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> npm run prettier:cli -- -l


> @loopback/example-todo@1.9.4 prettier:cli /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> lb-prettier "**/*.ts" "-l"


> @loopback/example-todo@1.9.4 eslint /Users/jannyhou/Desktop/2019/ui/test/loopback4-example-todo
> lb-eslint --report-unused-disable-directives .