Skip to content
Permalink
Branch: master
Find file Copy path
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
42 lines (27 sloc) 1.1 KB

disallow negating the left operand in in expressions (no-negated-in-lhs)

This rule was deprecated in ESLint v3.3.0 and replaced by the no-unsafe-negation rule.

Rule Details

Just as developers might type -a + b when they mean -(a + b) for the negative of a sum, they might type !key in object by mistake when they almost certainly mean !(key in object) to test that a key is not in an object.

Rule Details

This rule disallows negating the left operand in in expressions.

Examples of incorrect code for this rule:

/*eslint no-negated-in-lhs: "error"*/

if(!key in object) {
    // operator precedence makes it equivalent to (!key) in object
    // and type conversion makes it equivalent to (key ? "false" : "true") in object
}

Examples of correct code for this rule:

/*eslint no-negated-in-lhs: "error"*/

if(!(key in object)) {
    // key is not in object
}

if(('' + !key) in object) {
    // make operator precedence and type conversion explicit
    // in a rare situation when that is the intended meaning
}

When Not To Use It

Never.

You can’t perform that action at this time.