no-unsafe-negation

禁止对关系运算符的左操作数求反

配置文件 中的 "extends": "eslint:recommended" 属性启用了该规则

就像开发人员可能会在他们的意思是 -(a + b) 的负数时键入 -a + b 一样，当他们几乎可以肯定的意思是 !(key in object) 以测试某个键不在对象中时，他们可能会错误地键入 !key in object。!obj instanceof Ctor 类似。

规则详情

此规则不允许对以下关系运算符的左操作数取反：

• in 运算符。
• instanceof 运算符。

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/*eslint no-unsafe-negation: "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
}

if (!obj instanceof Ctor) {
    // operator precedence makes it equivalent to (!obj) instanceof Ctor
    // and it equivalent to always false since boolean values are not objects.
}

6RXgRVcYea97/4k5PNW/nItJttC+MHc4vVjxm8VW+ghbeqd3KsyvO/XAfiqXOEJI

/*eslint no-unsafe-negation: "error"*/

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

if (!(obj instanceof Ctor)) {
    // obj is not an instance of Ctor
}

异常

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6RXgRVcYea97/4k5PNW/nItJttC+MHc4vVjxm8VW+ghbeqd3KsyvO/XAfiqXOEJI

/*eslint no-unsafe-negation: "error"*/

if ((!foo) in object) {
    // allowed, because the negation is explicitly wrapped in parentheses
    // it is equivalent to (foo ? "false" : "true") in object
    // this is allowed as an exception for rare situations when that is the intended meaning
}

if(("" + !foo) in object) {
    // you can also make the intention more explicit, with type conversion
}

r6hi7htUov+vPER817DMpSRTvHu5NMFNJX5PKtsQSh4quBRUaItxaVoNlZcysCNG

/*eslint no-unsafe-negation: "error"*/

if (!(foo) in object) {
    // this is not an allowed exception
}

选项

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enforceForOrderingRelations

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/*eslint no-unsafe-negation: ["error", { "enforceForOrderingRelations": true }]*/

if (! a < b) {}

while (! a > b) {}

foo = ! a <= b;

foo = ! a >= b;

何时不使用

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