noUselessUndefined

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JavaScript (and super languages)

Summary

Rule available since: v2.0.0
Diagnostic Category: lint/nursery/noUselessUndefined
This rule has a safe fix.
The default severity of this rule is information.
Sources:
- Same as unicorn/no-useless-undefined

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noUselessUndefined": "error"
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      }
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    }
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  }
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}

Description

Disallow the use of useless undefined.

undefined is the default value for new variables, parameters, return statements, etc., so specifying it doesn’t make any difference.

Examples

Invalid

1
let foo = undefined;

code-block.js:1:11 lint/nursery/noUselessUndefined  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Don’t use unnecessary undefined.
  
  > 1 │ let foo = undefined;
      │           ^^^^^^^^^
    2 │ 
  
  ℹ undefined is the default value for new variables, parameters, return statements, etc… so specifying it doesn’t make any difference.
  
  ℹ Safe fix: Remove the undefined.
  
    1 │ let·foo·=·undefined;
      │         -----------

1
const {foo = undefined} = bar;

code-block.js:1:14 lint/nursery/noUselessUndefined  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Don’t use unnecessary undefined.
  
  > 1 │ const {foo = undefined} = bar;
      │              ^^^^^^^^^
    2 │ 
  
  ℹ undefined is the default value for new variables, parameters, return statements, etc… so specifying it doesn’t make any difference.
  
  ℹ Safe fix: Remove the undefined.
  
    1 │ const·{foo·=·undefined}·=·bar;
      │            -----------

1
const noop = () => undefined;

code-block.js:1:20 lint/nursery/noUselessUndefined  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Don’t use unnecessary undefined.
  
  > 1 │ const noop = () => undefined;
      │                    ^^^^^^^^^
    2 │ 
  
  ℹ undefined is the default value for new variables, parameters, return statements, etc… so specifying it doesn’t make any difference.
  
  ℹ Safe fix: Remove the undefined.
  
    1   │ - const·noop·=·()·=>·undefined;
      1 │ + const·noop·=·()·=>·{};
    2 2 │

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function foo() {
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   return undefined;
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}

code-block.js:2:11 lint/nursery/noUselessUndefined  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Don’t use unnecessary undefined.
  
    1 │ function foo() {
  > 2 │    return undefined;
      │           ^^^^^^^^^
    3 │ }
    4 │ 
  
  ℹ undefined is the default value for new variables, parameters, return statements, etc… so specifying it doesn’t make any difference.
  
  ℹ Safe fix: Remove the undefined.
  
    2 │ ···return·undefined;
      │           ---------

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function* foo() {
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  yield undefined;
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}

code-block.js:2:9 lint/nursery/noUselessUndefined  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Don’t use unnecessary undefined.
  
    1 │ function* foo() {
  > 2 │   yield undefined;
      │         ^^^^^^^^^
    3 │ }
    4 │ 
  
  ℹ undefined is the default value for new variables, parameters, return statements, etc… so specifying it doesn’t make any difference.
  
  ℹ Safe fix: Remove the undefined.
  
    2 │ ··yield·undefined;
      │         ---------

1
function foo(bar = undefined) {}

code-block.js:1:20 lint/nursery/noUselessUndefined  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Don’t use unnecessary undefined.
  
  > 1 │ function foo(bar = undefined) {}
      │                    ^^^^^^^^^
    2 │ 
  
  ℹ undefined is the default value for new variables, parameters, return statements, etc… so specifying it doesn’t make any difference.
  
  ℹ Safe fix: Remove the undefined.
  
    1 │ function·foo(bar·=·undefined)·{}
      │                  -----------

1
function foo({bar = undefined}) {}

code-block.js:1:21 lint/nursery/noUselessUndefined  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Don’t use unnecessary undefined.
  
  > 1 │ function foo({bar = undefined}) {}
      │                     ^^^^^^^^^
    2 │ 
  
  ℹ undefined is the default value for new variables, parameters, return statements, etc… so specifying it doesn’t make any difference.
  
  ℹ Safe fix: Remove the undefined.
  
    1 │ function·foo({bar·=·undefined})·{}
      │                   -----------

Valid

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let foo;
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const {foo} = bar;
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function foo() {
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  return;
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}
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function* foo() {
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  yield;
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}
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function foo(bar) {}
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function foo({bar}) {}
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foo();