equalityOperatorNegations

Reports negated expressions on the left side of equality checks.

✅ This rule is included in the ts preset.

Using a negated expression as the left operand of an equality check is almost always a mistake. The logical not operator (!) has higher precedence than equality operators, so !a === b is evaluated as (!a) === b, not !(a === b). This converts the left operand to a boolean before comparing, which is rarely the intended behavior.

Examples

❌ Incorrect

if (!value === true) {
  doSomething();
}

if (!count === 0) {
Error ts(2367)  ― This comparison appears to be unintentional because the types 'boolean' and 'number' have no overlap.
  handleEmpty();
}

✅ Correct

if (value !== true) {
  doSomething();
}

if (!(value === true)) {
  doSomething();
}

if (count !== 0) {
  handleEmpty();
}

Options

This rule is not configurable.

When Not To Use It

If you intentionally compare a negated boolean value with an equality operator, you may want to disable this rule. However, such code would be clearer if rewritten to use the opposite equality operator without the negation.

Further Reading

• MDN: Operator precedence
• MDN: Logical NOT

Equivalents in Other Linters

• ESLint: unicorn/no-negation-in-equality-check
• Oxlint: unicorn/no-negation-in-equality-check