no-unused-expressions warning for optional chaining #8107

iansan5653 · 2019-12-06T18:23:26Z

Describe the bug

I just upgrade react-scripts to 3.3.0. I am able to use nullish coalescing, but when I attempt to use optional chaining, I can't compile as I get this error:

./src/components/Select/Select.tsx
  Line 141:5:  Expected an assignment or function call and instead saw an expression  no-unused-expressions

Search for the keywords to learn more about each error.

The line in question is:

    this.props.onChange?.(resultingValue);

Did you try recovering your dependencies?

No, I don't have time at the moment. If this might help I'll try it.

Which terms did you search for in User Guide?

I searched for optional chaining, no-unused-expressions, eslint optional chaining.

Environment

npx: installed 91 in 30.467s

Environment Info:

  System:
    OS: Windows 10 10.0.17134
    CPU: (8) x64 Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz
  Binaries:
    Node: 12.2.0 - C:\Program Files\nodejs\node.EXE
    Yarn: Not Found
    npm: 6.9.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: 42.17134.1098.0
    Internet Explorer: 11.0.17134.1
  npmPackages:
    react: ^16.12.0 => 16.12.0
    react-dom: ^16.12.0 => 16.12.0
    react-scripts: 3.3.0 => 3.3.0
  npmGlobalPackages:
    create-react-app: Not Found

Steps to reproduce

Use optional chaining.
Attempt to run npm start.

Expected behavior

I expected the app to compile and for the code to function like:

    this.props.onChange !== undefined && this.props.onChange(resultingValue);

Actual behavior

The app failed to compile and gave the above message.

The text was updated successfully, but these errors were encountered:

heyimalex · 2019-12-06T22:23:37Z

It looks like those features just aren't currently supported by eslint? From #8003 it looks like we support using them with typescript, but until eslint lands support I'm not sure there's a solution. Take this with a grain of salt because I wasn't involved in landing those features.

iansan5653 · 2019-12-07T19:27:58Z

I knew it looked like an eslint error, but why are eslint errors preventing the page from rendering? I believe in linting but I'm not sure I can see a good reason for preventing compiling if there's a lint problem.

Until they add support, how can we disable this rule for CRA?

Your link is broken btw, correct link: eslint/eslint#12642

heyimalex · 2019-12-07T19:58:27Z

I think that you can't on a project level; we only support overriding with inline comments. You might be better off just not using optional chaining (unless you're using typescript) until a fix for this lands in eslint. I'm sorry, I know that isn't a great answer.

iansan5653 · 2019-12-07T20:00:06Z

Sorry, I should've mentioned this previously - I am using TypeScript. How can I make it work in that case?

heyimalex · 2019-12-07T20:48:16Z

You can only use it in typescript files. Using a fresh install with --template typescript and adding this to App.tsx doesn't emit an error for me.

const foo = {} as any;
foo.unknown?.();

Just to be clear, I can reproduce in js files.

danielkcz · 2019-12-13T09:21:21Z

Support already exists, you need to enable @typescript-eslint/no-unused-expressions instead of no-unused-expressions.

typescript-eslint/typescript-eslint#1241 (comment)

I tried when I enable typescript variant but keep regular one and sadly, it will complain. Only when that regular rule is explicitly disabled, it works correctly.

~~So shouldn't that rule be enabled in eslint-config-react-app instead? It should work for JS files just fine if I am not mistaken.~~

Oh I see it's been already done: #8003

josias-r · 2019-12-20T15:02:27Z

Just wanted to add, that you need TS < 3.7 for this to work, if that wasn't clear yet.
Optional chaining is working fine with my project.

danielkcz · 2019-12-20T15:29:31Z

@josias-r What? :) Optional chaining is a feature of TS 3.7. Whatever is working for you, might be because you have Babel somewhere in there 🤷‍♂

josias-r · 2019-12-22T15:20:19Z

@FredyC sorry meant to say TS 3.7 or higher. I have no special babel setup in my project. react-scripts 3.3.0 and prettier is installed and I can use optional chaining without problems in TSX files.

danielkcz · 2019-12-22T21:36:13Z

I think this issue can be closed now because eslint-config-react-app@5.1.0 is correctly using @typescript-eslint/no-unused-expressions for ts/tsx files.

heyimalex · 2019-12-22T22:21:56Z

I’m going to treat this as the tracking issue for optional chaining in non-typescript files, since that still isn’t supported afaik.

heyimalex · 2019-12-30T20:00:36Z

It looks like there's a workaround by using eslint-plugin-babel if anyone wants to try that out?

mofojed · 2020-04-17T20:20:07Z

I tried using eslint-plugin-babel but I was still getting the no-unused-expression error when running npm start (even with 'no-unused-expressions': 'off', set in .eslintrc)

RiZKiT · 2020-04-27T12:03:20Z

How about this solution: babel/eslint-plugin-babel#185 (comment)?

mofojed · 2020-04-27T13:51:31Z

@RiZKiT Yes I tried that solution, and I'm still seeing the error when running npm start.
I installed eslint-plugin-babel, added babel to the plugins section and the following to the rules section in .eslintrc:

    'no-unused-expressions': 'off',
    'babel/no-unused-expressions': 'error',

I still get the error when running npm start in my jsx file:

./src/console/notebook/Editor.jsx
  Line 44:5:  Expected an assignment or function call and instead saw an expression  no-unused-expressions

The line in question:

this.editor?.trigger('toggleFind', 'actions.find');

TheDSCPL · 2020-06-04T17:11:52Z

For Typescript, FredyC's answer is the solution. Thanks!
Nevertheless, there should be a way for the no-unused-expressions rule to work on vanilla JS because it is valid syntax when using the Babel plugin and in ECMAScript 2020.

taylankasap · 2020-06-21T16:02:45Z

@mofojed You're also supposed to use "parser": "babel-eslint" (I think)

Sleepful · 2020-07-03T09:52:38Z

@mofojed weird! it worked for me with:

    "no-unused-expressions": 0,
    "babel/no-unused-expressions": 1

do not forget to add to your eslintrc:

{
  "plugins": [
    "babel"
  ]
}

as the readme says

trdaya · 2020-07-31T14:16:11Z

@mofojed weird! it worked for me with:
    "no-unused-expressions": 0,
    "babel/no-unused-expressions": 1
do not forget to add to your eslintrc:
{
  "plugins": [
    "babel"
  ]
}
as the readme says

Sadly, not working for me

bradydowling · 2020-08-21T10:53:31Z

Seems like this should be working now for Typescript according to this issue (eslint/eslint#12822) but it's still not working for me so I probably need to update one of my dependencies, just don't want to go through the list right now.

Update: Just double checked that I have @typescript-eslint/parser 3.10.1 installed, which was released just a week ago so it should have the fix in it. Not sure what other packages I might need to update.

Update 2: After looking at the answer from @FredyC, I added the following to my eslint config and now I'm all set:

  "overrides": [
    {
      "files": ["**/*.tsx", "**/*.ts"],
      "rules": {
        "no-unused-expressions": "off",
      }
    }
  ],

KathyDinhTW · 2020-09-08T09:06:00Z

after upgrading typescript-eslint to latest version (v4.1.0) today, my app build also starts to fail with Expected an assignment or function call and instead saw an expression @typescript-eslint/no-unused-expressions for a line with optional chaining function call.
Overriding eslint config to turn off the rule did not work for me. Had to temporarily revert back to the old-fashioned conditional function call

"@typescript-eslint/eslint-plugin": "^4.1.0", "@typescript-eslint/parser": "^4.1.0",

koriner · 2020-09-10T22:09:36Z

Since updating to TS 4 & @typescript-eslint/* 4.1 this linting error seems to be impossible to stop when using optional chaining.

Expected an assignment or function call and instead saw an expression @typescript-eslint/no-unused-expressions is thrown regardless of whether we turn off the actual rule or not.

xumix · 2020-09-16T13:06:57Z

Same here, no matter what I do, @typescript-eslint/no-unused-expressions keeps popping up

peteschmitz · 2020-09-20T17:52:53Z

Also encountering an issue where optional-chaining typescript is throwing false-positives at build-time. Introduced after updating react-scripts (3.4.3), eslint, and typescript packages.

Settings via my .eslintrc file seem to run perfectly fine with eslint CLI. However, when I run react-scripts build I encounter the error @koriner mentioned at the first sight of an optional-chain.

I attempted to disable @typescript-eslint/no-unused-expressions and no-unused-expressions rules via the eslintConfig section in my package.json with no avail.

cglacet · 2020-09-22T11:06:37Z

@Sleepful It seems like it doesn't work for me, my .eslintrc:

{
    "parser": "babel-eslint",
    "plugins": [
        "babel"
    ],
    "extends": [
        "react-app",
    ],
    "rules": {
        "no-unused-expressions": "off",
        "babel/no-unused-expressions": "error"
    }
}

I get this error:

Expected an assignment or function call and instead saw an expression.eslint(babel/no-unused-expressions)

EDIT for some strange reason, if I remove everything from my .eslintrc, it just works, not sure what's causing the issue but I'll investigate.

Maybe "extends": ["react-app"] turn no-unused-expressions off. If I only remove my rules and this extends it works too.

TurboLion · 2020-10-16T11:24:07Z

if I remove everything from my .eslintrc, it just works, not sure what's causing the issue but I'll investigate.

Running into the same issue, but clearing .eslintrc didn't help.

@cglacet any luck with the investigation?

cglacet · 2020-10-16T13:16:54Z

@TurboLion no, sorry.

xumix · 2020-10-16T13:25:36Z

I've managed to mitigate the problem this way:

.eslintrc.json

"extends": ["react-app", "eslint:recommended"],
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "project": "tsconfig.json",
    "sourceType": "module"
  },
"plugins": ["react", "@typescript-eslint", "@typescript-eslint/eslint-plugin", "prefer-arrow"],
"rules": {
    "no-unused-expressions": "off",
    "@typescript-eslint/no-unused-expressions": "error"
}

package.json

"typescript": "^4.0.3",
    "@typescript-eslint/eslint-plugin": "^4.4.1",
    "@typescript-eslint/parser": "^4.4.1",
    "@typescript-eslint/typescript-estree": "^4.4.1",

remove node_modules and run npm install

scottdevito · 2020-10-18T06:41:08Z

I've managed to mitigate the problem this way:

.eslintrc.json

"extends": ["react-app", "eslint:recommended"],
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "project": "tsconfig.json",
    "sourceType": "module"
  },
"plugins": ["react", "@typescript-eslint", "@typescript-eslint/eslint-plugin", "prefer-arrow"],
"rules": {
    "no-unused-expressions": "off",
    "@typescript-eslint/no-unused-expressions": "error"
}

package.json

"typescript": "^4.0.3",
    "@typescript-eslint/eslint-plugin": "^4.4.1",
    "@typescript-eslint/parser": "^4.4.1",
    "@typescript-eslint/typescript-estree": "^4.4.1",

remove node_modules and run npm install

Tried this too (+ every other suggestion in this thread) but still can't get past the same no-unused-expressions error.

Paul6552 · 2020-10-24T10:18:23Z

@scottdevito
The solution for me was updating "react-scripts" to version 4. Maybe this can help, because i have the same eslintrc.json and package.json as you

k-funk · 2020-10-29T01:59:46Z

TLDR: npm run eject

Other than upgrading to 4.x, I think that most people's issues are because they are installing eslint plugins themselves, which is a good thing if you want to start improving code quality in your repo! But once you do that, you'll probably find yourself in the abyss since CRA doesn't let you turn off their implementation of eslint.

Part of the reason why you might be struggling to find out why your rule-overrides aren't working, is because CRA...wait for it... will cache your lint config! (noted in #9154 and #9007), making it even harder to debug where the issue lies with the convoluted mess of "who's really in control, and what version of each plugin is actually being used?".

While debugging, make sure you purge that cache in between runs:

rm -rf node_modules/.cache/eslint-loader && npm run build

Also note the undocumented (maybe it was at some point, but their docs aren't versioned so 🤷‍♂️ ) env var EXTEND_ESLINT=true that you must set in order for your custom rules to be read. Fortunately, that env var seems to be going away in 4.x.

My solution actually involves doing something you shouldn't do, and it'll probably bite me in the butt:

Setting EXTEND_ESLINT=true only in my .env.development, so that in prod it's not trying to run my new rules. Then the ugly part, which you should generally never do:

# package.json

  "dependencies": {
    "@typescript-eslint/eslint-plugin": "^2.34.0",
    "@typescript-eslint/parser": "^2.34.0",
    "react-scripts": "3.4.3",
    ...
  },
  "devDependencies": {
    "@typescript-eslint/eslint-plugin": "^4.5.0",
    "@typescript-eslint/parser": "^4.5.0",
    ...
  }

And then changing my production build from using npm ci to npm i to accommodate for my hack.

If I only list my upgrades devDependencies, my prod build (NODE_ENV=production npm ci && npm run build) will complain that unmet peerDependencies (@typescript-eslint/eslint-plugin) aren't met, and the linter will blow up during npm run build.

You might not run into this issue if you aren't checking in your package-lock.json and not using npm run ci during a prod build, but you probably should be.

All of this headache could be avoided if there was just an option to let people turn off the linter, at least during a production build.

Next on my plate: convincing my team that we will be okay if we eject.

jsdf · 2020-12-06T16:40:24Z

this issue seems to be fixed in react-scripts@4.0.0

Unsleeping · 2021-11-04T18:23:02Z

this issue seems to be fixed in react-scripts@4.0.0

it works for me, thank u

iansan5653 added issue: bug report needs triage labels Dec 6, 2019

heyimalex added tag: underlying tools and removed needs triage labels Dec 6, 2019

ianschmitz added this to the 3.3.1 milestone Dec 9, 2019

ianschmitz modified the milestones: 3.3.1, 3.4 Jan 31, 2020

iansu modified the milestones: 3.4, 3.5 Feb 14, 2020

petesantos mentioned this issue Mar 20, 2020

Alternate implementation of share workspace modal to match mocks [SATURN-1477] DataBiosphere/terra-ui#2078

Merged

07akioni mentioned this issue Jun 29, 2020

feat: render tab bar use panes react-component/tabs#291

Merged

pcardune mentioned this issue Sep 19, 2020

use typescript version of no-unused-expressions nori-dot-eco/nori-dot-com#28

Merged

raix modified the milestones: 5.1, 5.x Dec 17, 2021

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no-unused-expressions warning for optional chaining #8107

no-unused-expressions warning for optional chaining #8107

iansan5653 commented Dec 6, 2019

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Unsleeping commented Nov 4, 2021

no-unused-expressions warning for optional chaining #8107

no-unused-expressions warning for optional chaining #8107

Comments

iansan5653 commented Dec 6, 2019

Describe the bug

Did you try recovering your dependencies?

Which terms did you search for in User Guide?

Environment

Steps to reproduce

Expected behavior

Actual behavior

heyimalex commented Dec 6, 2019 • edited Loading

iansan5653 commented Dec 7, 2019

heyimalex commented Dec 7, 2019

iansan5653 commented Dec 7, 2019

heyimalex commented Dec 7, 2019

danielkcz commented Dec 13, 2019 • edited Loading

josias-r commented Dec 20, 2019

danielkcz commented Dec 20, 2019

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danielkcz commented Dec 22, 2019

heyimalex commented Dec 22, 2019

heyimalex commented Dec 30, 2019

mofojed commented Apr 17, 2020

RiZKiT commented Apr 27, 2020

mofojed commented Apr 27, 2020

TheDSCPL commented Jun 4, 2020

taylankasap commented Jun 21, 2020

Sleepful commented Jul 3, 2020

trdaya commented Jul 31, 2020

bradydowling commented Aug 21, 2020 • edited Loading

KathyDinhTW commented Sep 8, 2020

koriner commented Sep 10, 2020

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