no-negated-disjunction.md

no-negated-disjunction

Transforms the negation of a disjunction into the equivalent conjunction of negations according to De Morgan’s second law.

Rule Details

This rule enforces that when a disjunction is negated, the expression is rewritten according to De Morgan’s law. Instead of writing a negated disjunction like:

if (!(a || b)) {
  /* ... */
}

The rule suggests (and can auto-fix) the equivalent form:

if (!a && !b) {
  /* ... */
}

Why Use This Rule?

Negated disjunctions can sometimes be less clear or counterintuitive. Transforming them into a conjunction of negations makes the logic explicit:

• It clearly indicates that both conditions must be false.
• It may help avoid mistakes in complex boolean logic by making the individual conditions more explicit.

When Is the Rule Applied?

• The rule applies only when the operand of the negation is a pure disjunction — that is, when all operands are combined with || at the same nesting level.
• If the expression inside the negation contains a mix of logical operators (for example, !(a || b && c)), the rule will not apply the transformation.

Auto-fix

This rule is auto-fixable. When applied, it automatically rewrites code such as:

const foo = !(a || !b || c >= 10)

To:

const foo = !a && b && c < 10

Options

This rule has no options.

Related Rules

• no-negated-conjunction — A similar rule for transforming the negation of a conjunction (!(A && B)) into the equivalent disjunction of negations (!A || !B), based on De Morgan’s first law.

Resources

• Rule Source
• Test Source