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

Answer 1

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

1. argsIgnorePattern

2. 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

Answer 2

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.

Answer 3

Extend the tsconfig.json with dev.tsconfig.json

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

This will deisable the unused variable and unused parameter in development

Inside dev.tsconfig.json:

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

Answer 4

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.

Answer 5

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

Answer 6

First turn off noUnusedLocals in tsconfig.json:

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

Then fix eslint rules in .eslintrc.js:

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

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'],
  },
],