no-negated-in-lhs

Disallow negating the left operand in in expressions

此规则在 ESLint v3.3.0 中废弃并被 no-unsafe-negation 规则所取代。

就像开发者可能会输入 -a + b，而他们的意思是 -(a + b) 表示一个和的负数，他们可能会错误地输入 !key in object，而他们几乎肯定是指 !(key in object) 来测试一个键不在一个对象中。

规则细节

这条规则不允许在 in 表达式中否定左边的操作数。

使用此规则的错误示例：

/*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
}
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使用此规则的正确示例：

/*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
}
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何时不用

绝不要。

Version

This rule was introduced in ESLint v0.1.2.

Resources

• Rule source
• Tests source