Avoid negating the left operand of relational operators

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Metadata

ID: javascript-best-practices/no-unsafe-negation

Language: JavaScript

Severity: Warning

Category: Best Practices

Description

Negation of the left-hand side of an expression is often unintended.

Non-Compliant Code Examples

!a in b
(!a in b)
!(a) in b
!a instanceof b
(!a instanceof b)
!(a) instanceof b

Compliant Code Examples

a in b
a in b === false
!(a in b);
(!a) in b
a instanceof b
a instanceof b === false;
!(a instanceof b);
(!a) instanceof b;

How to use this rule

1
2
rulesets:
  - javascript-best-practices     # Rules to enforce JavaScript best practices.

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