noSparseArray

JavaScript (and super languages)

Summary

Rule available since: v1.0.0
Diagnostic Category: lint/suspicious/noSparseArray
This rule is recommended, which means is enabled by default.
This rule has an unsafe fix.
The default severity of this rule is error.
Sources:
- Same as no-sparse-arrays

How to configure

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{
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  "linter": {
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    "rules": {
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      "suspicious": {
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        "noSparseArray": "error"
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      }
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    }
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  }
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}

Description

Prevents the use of sparse arrays (arrays with holes).

Sparse arrays may contain empty slots due to the use of multiple commas between two items, like the following:

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const items = [a,,b];

Arrays with holes might yield incorrect information. For example, the previous snippet, items has a length of 4, but did the user really intended to have an array with four items? Or was it a typo.

This rule enforce the user to explicitly an undefined in places where there’s a hole.

Examples

Invalid

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[1,,2]

code-block.js:1:1 lint/suspicious/noSparseArray  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This array contains an empty slots..
  
  > 1 │ [1,,2]
      │ ^^^^^^
    2 │ 
  
  ℹ The presences of empty slots may cause incorrect information and might be a typo.
  
  ℹ Unsafe fix: Replace hole with undefined
  
    1 │ [1,·undefined,2]
      │    ++++++++++

Valid

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[1, undefined, 2]