noMagicArrayFlatDepth (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.4
Diagnostic Category: lint/nursery/noMagicArrayFlatDepth
This rule doesn’t have a fix.
The default severity of this rule is information.
Sources:
- Same as unicorn/no-magic-array-flat-depth

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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        "noMagicArrayFlatDepth": "error"
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      }
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    }
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  }
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}

Description

Disallow unexplained numbers as the depth argument of Array.prototype.flat().

The depth passed to flat() is usually 1 (the default) or Infinity. Any other number doesn’t say why the array needs to be flattened to that exact depth. Store the depth in a variable with a descriptive name, or add a comment inside the parentheses that explains it.

Examples

Invalid

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const items = array.flat(2);

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

  ℹ The depth passed to flat() is an unexplained number.
  
  > 1 │ const items = array.flat(2);
      │                          ^
    2 │ 
  
  ℹ A bare number doesn't say why the array needs to be flattened to this depth.
  
  ℹ Store the depth in a variable with a descriptive name, or add a comment inside the parentheses that explains it.
  
  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.

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const items = array.flat(99);

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

  ℹ The depth passed to flat() is an unexplained number.
  
  > 1 │ const items = array.flat(99);
      │                          ^^
    2 │ 
  
  ℹ A bare number doesn't say why the array needs to be flattened to this depth.
  
  ℹ Store the depth in a variable with a descriptive name, or add a comment inside the parentheses that explains it.
  
  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.

Valid

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const items = array.flat();
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const allItems = array.flat(Infinity);
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const allValues = array.flat(Number.POSITIVE_INFINITY);
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const rows = array.flat(depth);
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const cells = array.flat(/* The grid is always two levels deep. */ 2);