disallow negating the left operand of relational operators (no-unsafe-negation)

禁止对关系运算符的左操作数使用否定操作符 (no-unsafe-negation)

The "extends": "eslint:recommended" property in a configuration file enables this rule.

配置文件中的 "extends": "eslint:recommended" 属性启用了此规则。

The --fix option on the command line can automatically fix some of the problems reported by this rule.

命令行中的 --fix 选项可以自动修复一些该规则报告的问题。

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.

开发人员可能会把 -(a + b) 写错成 -a + b 来表示一个负数，也可能会把 !(key in object) 错写成 !key in object 来测试一个键是否在对象中。类似的情况也有 !obj instanceof Ctor。

Rule Details

This rule disallows negating the left operand of Relational Operators.

该规则禁止对关系运算符的左操作数使用否定操作符。

Relational Operators are:

关系运算符有：

Examples of incorrect code for this rule:

错误 代码示例：

/*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.
}

Examples of correct code for this rule:

正确 代码示例：

/*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
}

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

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

如果你不想收到不安全的逻辑否，可以不使用此规则。

Version

This rule was introduced in ESLint 3.3.0.

该规则在 ESLint 3.3.0 中被引入。

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