tslint how to disable error "someVariable is declared but its value is never read"

Question

I'm using tslint, and got the error.

'myVariable' is declared but its value is never read.

I went to the website that documents the rules https://palantir.github.io/tslint/rules/ and searched for the string is declared but its value is never read but didn't find that text. While I can and did look for settings that might be tied to this error, it shouldn't be a guessing game.

What is the configuration change needed to suppress/stop this error?

Just as importantly, when I get an error in tslint that says "this happened" how can I find what setting is used to configure or change the tslint behavior on how to handle that error?

I also did a search on the website (google search I used was)

site:palantir.github.io  is declared but its value is never read

but a direct hit did not appear, so the answer might be on the palantir.github.io website but I just didn't (yet) find it.

How do others find the tslint variable/configuration settings that change to suppress a particular error?

Please refrain from suggesting I comment out the code that is causing the problem. I'm looking for an answer to my more general question as well as to the specific question. Thank you.

Have you tried setting `noUnusedLocals` to `false` in your `compilerOptions` ? Recommended by this post: https://github.com/Microsoft/TypeScript/issues/19700#issuecomment-382469957 — rickjerrity, Apr 24 '18 at 22:20
"noUnusedLocals" : false, + "noUnusedParameters": false, worked for me — Gregor, Sep 06 '19 at 14:12
as if you would like to have a ferrari with a bunch of loose / unused pieces in the engine :) — eduardomoroni, Oct 02 '20 at 10:10

score 145 · Answer 1 · edited May 10 '22 at 09:27

145

Any parameter name starting with _ is exempt from the check. Use _myVariable instead of myvariable to remove this warning.

edited May 10 '22 at 09:27

Jaroslav Bezděk

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answered Aug 29 '18 at 20:00

Rachit Rawat

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It does not happen automatically, you have to specify ignore pattern. `"no-unused-variable": [true, {"ignore-pattern": "^_"}]` But yes, this is a good solution. – Soumya Kanti Sep 17 '18 at 05:15
6

I didn't have to specify that pattern, worked for me right away – JP Lew Dec 06 '18 at 19:29
8

As an update, `"no-unused-variable"` is deprecated since TypeScript 2.9 https://github.com/palantir/tslint/issues/4046 – Adi Fatol Jan 31 '19 at 10:07
3

Worth noting that since tslint is deprecated, you should use eslint and typescript-eslint instead. Using _ does not automatically bypass that rule no-unused-vars, but requires configuration like Rachit said. https://eslint.org/docs/rules/no-unused-vars. Using _ still does bypass the TS compiler automatically. – Thad Peiffer Jan 17 '20 at 14:51
The current preferred way to implement this (to the best of my knowledge) is, in your `.eslintrc.js` file: ` '@typescript-eslint/no-unused-vars': ['error', { 'argsIgnorePattern': '^_' }],` use `argsIgnorePattern` if referring to arguments in something like a decorator, and/or `varsIgnorePattern` to ignore declared variables. – Eric_WVGG Aug 03 '20 at 17:06

score 82 · Accepted Answer · edited Apr 08 '21 at 13:04

82

Fist question:

Edit the file:tsconfig.json, adding/modifying key "noUnusedLocals": false.

You'll need to restart the server.

Second question:

If it is a tslint error; VS Code shows, in the error message, the rule that's been applied.

Identifier 'doc' is never reassigned; use 'const' instead of 'let'. (prefer-const)

The prefer-const rule in this case.

edited Apr 08 '21 at 13:04

Liam

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answered Apr 28 '18 at 21:40

Roger

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Or you can apparently [declare variables you only use in the template `protected`](https://github.com/Microsoft/TypeScript/issues/19700#issuecomment-348950146) rather than turning off checking for any unused locals. – ruffin Jul 23 '18 at 16:12

score 46 · Answer 3 · answered Sep 03 '18 at 07:18

46

Add this line just before the line which causes the error:

  /* tslint:disable:no-unused-variable */

You will no longer receive the tslint error message.

This is a better solution than turning off the error for you whole codebase in tslint.conf because then it wouldn't catch variables that really aren't used.

answered Sep 03 '18 at 07:18

edwin

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But what would be the command to disable next line with eslint? – Raphael Pinel Jun 15 '23 at 08:32
Raphael: see https://eslint.org/docs/latest/rules/no-unused-vars – edwin Jun 16 '23 at 09:10

Masih Jahangiri · Answer 4 · 2022-01-17T16:59:22.170

41

New solution

First, turn off noUnusedLocals in tsconfig.json:

{
  "compilerOptions": {
    "noUnusedLocals": false,
  }
}

Then fix eslint rules in .eslintrc.js:

module.exports = {
  rules: {
    'no-unused-vars': 'off',
    '@typescript-eslint/no-unused-vars': ['error', { 'varsIgnorePattern': '^_', "argsIgnorePattern": "^_" }],
  },
};

And If using @typescript-eslint/naming-convention rule should add leadingUnderscore: 'allow', For example, if you are using Airbnb config:

'@typescript-eslint/naming-convention': [
  'error',
  {
    selector: 'variable',
    format: ['camelCase', 'PascalCase', 'UPPER_CASE'],
    leadingUnderscore: 'allow',
  },
  {
    selector: 'function',
    format: ['camelCase', 'PascalCase'],
  },
  {
    selector: 'typeLike',
    format: ['PascalCase'],
  },
],

Note: you should update all related eslint packages in package.json to the latest version manually.

edited Jan 17 '22 at 16:59

answered Apr 16 '20 at 21:14

Masih Jahangiri

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1

Why hadn't it worked for me? I've put noUnusedLocals and noUnusedParameters to false in tsconfig.json. But VSCode still shows the ts(6133) error alongside the eslint warning in the popup window on hover. I'm using nuxt with takeover mode – Seangle Oct 11 '22 at 12:39
@Seangle I have the same issue: Search for `unused` in your VS Code settings and turn it off. Personally, I like it on there, so I'm trying to figure out a way to only turn it off for a single line. – Daniel Kaplan Apr 18 '23 at 23:15

score 12 · Answer 5 · edited Apr 21 '22 at 23:04

12

Extend the tsconfig.json with dev.tsconfig.json

And run the command tsc -p ./dev.tsconfig.json

This will disable the unused variable and unused parameter in development

Inside dev.tsconfig.json:

{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "noUnusedLocals": false,
    "noUnusedParameters": false,
   }
}

edited Apr 21 '22 at 23:04

PatS

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answered Nov 12 '20 at 19:11

anandharshan

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Thanks it was the noUnusedParameters that was screwing me over – 55 Cancri Nov 28 '21 at 17:23

score 5 · Answer 6 · answered Oct 17 '18 at 18:20

I am using typescript": "2.9.1" with tslint": "^5.10.0.

I was getting tons of error such as

Property 'logger' is declared but its value is never read.

Also, I observed that I was getting a warning when running ng-lint

$> ng lint
no-unused-variable is deprecated. Since TypeScript 2.9. Please use the built-in compiler checks instead.

So, I removed the no-unused-variable rule fromt tslint.json - and that seems to solve the problem for me.

score 3 · Answer 7 · edited Feb 05 '20 at 17:33

3

There are two type of variables and you can do it in two ways

argsIgnorePattern
varsIgnorePattern
- no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]
- no-unused-vars: ["error", { "varsIgnorePattern": "^_" }]

Both these rule in eslint will ignore any function arguments and variables that starts with _ sign respectively

edited Feb 05 '20 at 17:33

Kalana

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answered Feb 05 '20 at 17:31

HexaCrop

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score 3 · Answer 8 · answered Apr 19 '23 at 00:44

There are many reasons you could be getting this error/warning:

Your tsconfig.json needs to default/disable noUnusedLocals and noUnusedParameters.
Your .eslintrc.json needs to set "@typescript-eslint/no-unused-vars": ["off"],.
(And I haven't seen this one mentioned yet:) Your VSCode setting named "editor.showUnused" may be set to true. It overwrites these tsconfig.json and .eslintrc.json settings, at least in my workspace.

You can find this setting by searching for "unused":

For me, I actually want this warning most of the time* but not always. Unfortunately, none of the comment hints seem to work on this vscode setting. The only workarounds/hack I've found is to put an export in front of it or remove all the other exports in the file.

* Maybe that's a good reason to turn it on everywhere, something I'll try later.

score 1 · Answer 9 · edited Mar 29 '21 at 06:06

I saw a solution on this web site: https://phpenthusiast.com/blog/angular-form-ngform-and-two-ways-data-binding.

it helped me but only 50% of it

This is my modified code:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';// i added this line and one more line.
import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';

import { DheerajComponent } from './dheeraj/dheeraj.component'
@NgModule({
  declarations: [
    AppComponent,
    DheerajComponent
  ],
  imports: [
    BrowserModule,
    AppRoutingModule, 
    FormsModule, // this one. remaining all default code
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { 
}

score 1 · Answer 10 · answered Sep 16 '21 at 06:52

1

In react if you have some thing like this

export default class Body extends Component {
    
    let data = null; // somethings like this line

    // ...
    // ...

convert it to

export default class Body extends Component {
    
    data = null; // somethings like this line

    // ...
    // ...

answered Sep 16 '21 at 06:52

Bambier

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Just remove `let` or `const` or `var` – Bambier Sep 16 '21 at 06:53

d.k · Answer 11 · 2022-02-22T09:56:17.070

0

If someone needs to disable it just for a moment, when developing, the best way may be to just run the tsc compiler with an additional command line flag:

$npx tsc -w --noUnusedLocals false --noUnusedParameters false

edited Feb 22 '22 at 09:56

answered Feb 22 '22 at 09:22

d.k

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score -2 · Answer 12 · answered Mar 05 '19 at 12:57

-2

Another way to avoid this is to create a get-method for every variable you have, like this:

get variablename():variabletype{return this.variablename;}

answered Mar 05 '19 at 12:57

Jorgé Reyniers

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6

6

This adds potentially unnecessary code to fix a linter warning. Much better to actually configure the linter to your liking than to add unused code. – Enmanuel Rivera Mar 24 '19 at 15:32
1

This is no unnecessary code if you work with classes with private properties. – Jorgé Reyniers Mar 25 '19 at 16:50

tslint how to disable error "someVariable is declared but its value is never read"

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