useIncludes

JavaScript (and super languages)

Summary

Diagnostic Category: lint/nursery/useIncludes
This rule has an unsafe fix.
The default severity of this rule is information.
This rule belongs to the following domains:
- types
Sources:
- Inspired from @typescript-eslint/prefer-includes

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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        "useIncludes": "error"
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      }
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    }
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  }
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}

Description

Prefer Array#includes() over Array#indexOf() checks.

Array#indexOf() returns a numeric index and is commonly compared against -1 to check for the presence of an element. Array#includes() is more readable and expressive for this purpose, and avoids off-by-one mistakes with the comparison operator.

Examples

Invalid

1
const arr = [1, 2, 3];
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arr.indexOf(1) !== -1;

/invalid1.ts:2:1 lint/nursery/useIncludes  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Checking the result of indexOf() against -1 to test for presence.
  
    1 │ const arr = [1, 2, 3];
  > 2 │ arr.indexOf(1) !== -1;
      │ ^^^^^^^^^^^^^^^^^^^^^
    3 │ 
  
  ℹ indexOf() returns a numeric index, not a boolean. Comparing it against -1 is error-prone and harder to read.
  
  ℹ Use includes() instead, which directly expresses the intent and returns a boolean.
  
  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: Replace with .includes().
  
    1 1 │   const arr = [1, 2, 3];
    2   │ - arr.indexOf(1)·!==·-1;
      2 │ + arr.includes(1);
    3 3 │

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const arr = [1, 2, 3];
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arr.indexOf(1) >= 0;

/invalid2.ts:2:1 lint/nursery/useIncludes  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Checking the result of indexOf() against -1 to test for presence.
  
    1 │ const arr = [1, 2, 3];
  > 2 │ arr.indexOf(1) >= 0;
      │ ^^^^^^^^^^^^^^^^^^^
    3 │ 
  
  ℹ indexOf() returns a numeric index, not a boolean. Comparing it against -1 is error-prone and harder to read.
  
  ℹ Use includes() instead, which directly expresses the intent and returns a boolean.
  
  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: Replace with .includes().
  
    1 1 │   const arr = [1, 2, 3];
    2   │ - arr.indexOf(1)·>=·0;
      2 │ + arr.includes(1);
    3 3 │

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const arr = [1, 2, 3];
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arr.indexOf(1) === -1;

/invalid3.ts:2:1 lint/nursery/useIncludes  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Checking the result of indexOf() against -1 to test for presence.
  
    1 │ const arr = [1, 2, 3];
  > 2 │ arr.indexOf(1) === -1;
      │ ^^^^^^^^^^^^^^^^^^^^^
    3 │ 
  
  ℹ indexOf() returns a numeric index, not a boolean. Comparing it against -1 is error-prone and harder to read.
  
  ℹ Use !…includes() instead, which directly expresses the intent and returns a boolean.
  
  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: Replace with !…includes().
  
    1 1 │   const arr = [1, 2, 3];
    2   │ - arr.indexOf(1)·===·-1;
      2 │ + !
      3 │ + arr.includes(1);
    3 4 │

Valid

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const arr = [1, 2, 3];
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arr.includes(1);

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const arr = [1, 2, 3];
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// Positional use of indexOf is fine
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const pos = arr.indexOf(1);