noNegatedArrayPredicate (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.6
Diagnostic Category: lint/nursery/noNegatedArrayPredicate
This rule has an unsafe fix.
The default severity of this rule is information.
Sources:
- Same as unicorn/no-negated-array-predicate

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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        "noNegatedArrayPredicate": "error"
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      }
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    }
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  }
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}

Description

Disallow negating the result of Array#some() or Array#every().

!array.some(callback) checks that no item passes the test, which is the same as checking that every item fails it: array.every((item) => !callback(item)). In the same way, !array.every(callback) is the same as array.some((item) => !callback(item)).

Putting the ! inside the callback function keeps the condition next to the test it changes, and two ! operators that cancel each other out, as in !array.some((item) => !item.done), can be removed entirely: array.every((item) => item.done).

The rule only reports calls whose callback function returns a single expression, either directly, as in (item) => item.done, or with one return statement.

Examples

Invalid

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const isMissing = !array.some((item) => isUnicorn(item));

code-block.js:1:26 lint/nursery/noNegatedArrayPredicate  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ The result of some() is negated with !.
  
  > 1 │ const isMissing = !array.some((item) => isUnicorn(item));
      │                          ^^^^
    2 │ 
  
  ℹ Negating the whole call hides the condition that is actually checked. Calling every() with a negated callback function gives the same result and is easier to read.
  
  ℹ Remove the ! before the call, use every() instead, and negate the value that the callback function returns.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use every() with a negated callback function.
  
    1   │ - const·isMissing·=·!array.some((item)·=>·isUnicorn(item));
      1 │ + const·isMissing·=·array.every((item)·=>·!isUnicorn(item));
    2 2 │

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const isNotEveryUnicorn = !array.every((item) => isUnicorn(item));

code-block.js:1:34 lint/nursery/noNegatedArrayPredicate  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ The result of every() is negated with !.
  
  > 1 │ const isNotEveryUnicorn = !array.every((item) => isUnicorn(item));
      │                                  ^^^^^
    2 │ 
  
  ℹ Negating the whole call hides the condition that is actually checked. Calling some() with a negated callback function gives the same result and is easier to read.
  
  ℹ Remove the ! before the call, use some() instead, and negate the value that the callback function returns.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use some() with a negated callback function.
  
    1   │ - const·isNotEveryUnicorn·=·!array.every((item)·=>·isUnicorn(item));
      1 │ + const·isNotEveryUnicorn·=·array.some((item)·=>·!isUnicorn(item));
    2 2 │

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if (!array.some((item) => !isUnicorn(item))) {}

code-block.js:1:12 lint/nursery/noNegatedArrayPredicate  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ The result of some() is negated with !.
  
  > 1 │ if (!array.some((item) => !isUnicorn(item))) {}
      │            ^^^^
    2 │ 
  
  ℹ Negating the whole call hides the condition that is actually checked. Calling every() with a negated callback function gives the same result and is easier to read.
  
  ℹ Remove the ! before the call, use every() instead, and negate the value that the callback function returns.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.
  
  ℹ Unsafe fix: Use every() with a negated callback function.
  
    1   │ - if·(!array.some((item)·=>·!isUnicorn(item)))·{}
      1 │ + if·(array.every((item)·=>·isUnicorn(item)))·{}
    2 2 │

Valid

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const isMissing = array.every((item) => !isUnicorn(item));
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const isNotEveryUnicorn = array.some((item) => !isUnicorn(item));
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if (array.every((item) => isUnicorn(item))) {}
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// The callback function isn't written inline, so there's nothing to negate.
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if (!array.every(Boolean)) {}