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no-unmatchable-selectors.md

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no-unmatchable-selectors

Disallow unmatchable selectors.

Background

An unmatchable selector is one that can never match any element in any document. These are effectively dead code and usually indicate mistakes.

For example:

  • a:nth-child(0) — the An+B formula never produces a positive position (≥ 1).
  • a:nth-child(-n) — a negative step with no offset never yields a positive position.

Rule Details

This rule reports selectors that can never match any element.

It currently checks:

  • :nth-*() pseudo-classes whose An+B formulas cannot produce a positive position (≥ 1).

Examples of incorrect code:

/* eslint css/no-unmatchable-selectors: "error" */

a:nth-child(0) {}
a:nth-child(-n) {}
a:nth-last-child(0 of .active) {}
a:nth-of-type(0n) {}
a:nth-last-of-type(0n+0) {}

Examples of correct code:

/* eslint css/no-unmatchable-selectors: "error" */

a:nth-child(1) {}
a:nth-child(even) {}
a:nth-child(odd) {}
a:nth-last-child(1 of .active) {}
a:nth-of-type(1n) {}
a:nth-last-of-type(1n+0) {}

When Not to Use It

If you intentionally use selectors that can never match (for example, as temporary placeholders during development), then you can safely disable this rule.

Prior Art