Disallow negated left operand of in operator (no-negated-in-lhs)

Rule Details

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


Further Reading



This rule was introduced in ESLint 0.1.2.