Index

no-unsafe-negation

不允许否定关系运算符的左操作数

✅

在 配置文件 中使用来自 @eslint/js 的 recommended 配置可以启用此规则

💡

此规则报告的一些问题可通过编辑器 建议 手动修复

就像开发者在想表达某个和的负值时可能会输入 -a + b 而实际上想输入 -(a + b)，他们几乎肯定是想输入 !(key in object) 来测试一个键是否不在对象中时，也可能会错误地输入 !key in object。!obj instanceof Ctor 也类似。

🌐 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. !obj instanceof Ctor is similar.

规则详情

🌐 Rule Details

此规则不允许对以下关系运算符的左操作数取反：

🌐 This rule disallows negating the left operand of the following relational operators:

此规则的错误代码示例：

🌐 Examples of incorrect code for this rule:

在线运行 
/*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.
}

符合此规则的正确代码示例：

🌐 Examples of correct code for this rule:

在线运行 
/*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

🌐 Exception

对于在罕见情况下有意对左操作数取反的，本规则允许例外。如果整个取反明确地用括号括起来，规则将不会报告问题。

🌐 For rare situations when negating the left operand is intended, this rule allows an exception. If the whole negation is explicitly wrapped in parentheses, the rule will not report a problem.

符合此规则的正确代码示例：

🌐 Examples of correct code for this rule:

在线运行 
/*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
}

此规则的错误代码示例：

🌐 Examples of incorrect code for this rule:

在线运行 
/*eslint no-unsafe-negation: "error"*/

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

选项

🌐 Options

此规则有一个对象选项：

🌐 This rule has an object option:

  • "enforceForOrderingRelations": false（默认）允许对排序关系运算符（<、>、<=、>=）的左侧进行取反
  • "enforceForOrderingRelations": true 不允许对排序关系运算符的左侧进行取反

enforceForOrderingRelations

将此选项设置为 true 时，该规则还将强制适用于：

🌐 With this option set to true the rule is additionally enforced for:

  • < 操作符。
  • > 操作符。
  • <= 操作符。
  • >= 操作符。

目的是避免使用诸如 ! a < b（其等同于 (a ? 0 : 1) < b）的表达，而实际上真正想表达的是 !(a < b)。

🌐 The purpose is to avoid expressions such as ! a < b (which is equivalent to (a ? 0 : 1) < b) when what is really intended is !(a < b).

使用 { "enforceForOrderingRelations": true } 选项时，该规则的其他 错误 代码示例：

🌐 Examples of additional incorrect code for this rule with the { "enforceForOrderingRelations": true } option:

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

if (! a < b) {}

while (! a > b) {}

foo = ! a <= b;

foo = ! a >= b;

何时不使用

🌐 When Not To Use It

如果你不想通知不安全的逻辑否定，那么禁用此规则是安全的。

🌐 If you don’t want to notify unsafe logical negations, then it’s safe to disable this rule.

由 TypeScript 处理

使用 TypeScript 时禁用此规则是安全的，因为 TypeScript 的编译器强制执行此检查。

版本

此规则是在 ESLint v3.3.0 中引入。

资源