Disallow negated left operand of
in operator (no-negated-in-lhs)
This error is raised to highlight a potential error. Commonly, when a developer intends to write
if(!(a in b)) // do something
they will instead write
if(!a in b) // do something
If one intended the original behaviour, the left operand should be explicitly coerced to a string like below.
if(('' + !a) in b) // do something
When Not To Use It
This rule was introduced in ESLint 0.1.2.