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 --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.


Relational Operators are:


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.



This rule was introduced in ESLint 3.3.0.

该规则在 ESLint 3.3.0 中被引入。