useBetterDomTraversing (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.5.13
Diagnostic Category: lint/nursery/useBetterDomTraversing
This rule has an unsafe fix.
The default severity of this rule is information.
Sources:
- Inspired from unicorn/better-dom-traversing

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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        "useBetterDomTraversing": "error"
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      }
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    }
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  }
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}

Description

Prefer modern DOM traversal APIs over positional indexes and chained walks.

Named first-child accessors, querySelector(), and closest() describe intent more clearly than childNodes[0], children[n], and repeated .parentElement access. Merging chained .querySelector() calls with static selectors has the same benefit.

Fixes are unsafe because the replacement is not always equivalent:

.childNodes[0] is undefined when empty; .firstChild is null
.closest() looks for any matching ancestor, not an exact number of .parentElement hops
chained .querySelector() calls search inside the first match, while a combined selector searches from the original node

props.children is ignored because that is component data, not DOM traversal.

Examples

Invalid

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element.childNodes[0];

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

  ℹ This indexes .childNodes to get the first child.
  
  > 1 │ element.childNodes[0];
      │ ^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ A positional index is harder to read than a named first-child accessor.
  
  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 .firstChild instead.
  
    1   │ - element.childNodes[0];
      1 │ + element.firstChild;
    2 2 │

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element.children[0];

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

  ℹ This indexes .children to get the first element child.
  
  > 1 │ element.children[0];
      │ ^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ A positional index is harder to read than a named first-child accessor.
  
  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 .firstElementChild instead.
  
    1   │ - element.children[0];
      1 │ + element.firstElementChild;
    2 2 │

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element.children[2];

code-block.js:1:1 lint/nursery/useBetterDomTraversing ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This uses a positional index on .children.
  
  > 1 │ element.children[2];
      │ ^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ A CSS selector describes which child you want without relying on a numeric index.
  
  ℹ Replace this with .querySelector() and a selector for the child.
  
  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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element.parentElement.parentElement;

code-block.js:1:1 lint/nursery/useBetterDomTraversing ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This walks ancestors by chaining .parentElement.
  
  > 1 │ element.parentElement.parentElement;
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ .closest() looks up a matching ancestor without repeating .parentElement.
  
  ℹ Replace this chain with .closest() and a selector for the ancestor.
  
  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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element.querySelector("a").querySelector("b");

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

  ℹ These .querySelector() calls are chained.
  
  > 1 │ element.querySelector("a").querySelector("b");
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ One .querySelector() call with a combined selector is easier to read.
  
  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: Merge the .querySelector() calls.
  
    1   │ - element.querySelector("a").querySelector("b");
      1 │ + element.querySelector(":scope·a·b");
    2 2 │

Valid

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element.firstChild;
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element.firstElementChild;
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element.querySelector("li");
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element.closest("form");
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const child = props.children[0];