no-cond-assign

禁止条件表达式中的赋值运算符

在条件语句中，很容易将比较运算符（例如 ==）误输入为赋值运算符（例如 =）。例如：

🌐 In conditional statements, it is very easy to mistype a comparison operator (such as ==) as an assignment operator (such as =). For example:

// Check the user's job title
if (user.jobTitle = "manager") {
    // user.jobTitle is now incorrect
}
1
2
3
4

在条件语句中使用赋值运算符是有正当理由的。然而，要判断某个特定的赋值是否是有意的，可能很困难。

🌐 There are valid reasons to use assignment operators in conditional statements. However, it can be difficult to tell whether a specific assignment was intentional.

规则详情

🌐 Rule Details

此规则禁止在 if、for、while 和 do...while 语句的测试条件中使用模糊的赋值运算符。

🌐 This rule disallows ambiguous assignment operators in test conditions of if, for, while, and do...while statements.

选项

🌐 Options

此规则有一个字符串选项：

🌐 This rule has a string option:

• "except-parens"（默认）仅在赋值被括号括起来的情况下才允许在测试条件中进行赋值（例如，为了允许在 while 或 do...while 循环的测试中重新赋值一个变量）。
• "always" 不允许在测试条件中进行所有赋值。

except-parens

使用默认 "except-parens" 选项时，该规则的错误代码示例：

🌐 Examples of incorrect code for this rule with the default "except-parens" option:

/*eslint no-cond-assign: "error"*/

// Unintentional assignment
let x;
if (x = 0) {
    const b = 1;
}

// Practical example that is similar to an error
const setHeight = function (someNode) {
    do {
        someNode.height = "100px";
    } while (someNode = someNode.parentNode);
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14

使用默认 "except-parens" 选项时，该规则的正确代码示例：

🌐 Examples of correct code for this rule with the default "except-parens" option:

/*eslint no-cond-assign: "error"*/

// Assignment replaced by comparison
let x;
if (x === 0) {
    const b = 1;
}

// Practical example that wraps the assignment in parentheses
const setHeight = function (someNode) {
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode));
}

// Practical example that wraps the assignment and tests for 'null'
const set_height = function (someNode) {
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode) !== null);
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

always

使用 "always" 选项时违反此规则的错误代码示例：

🌐 Examples of incorrect code for this rule with the "always" option:

/*eslint no-cond-assign: ["error", "always"]*/

// Unintentional assignment
let x;
if (x = 0) {
    const b = 1;
}

// Practical example that is similar to an error
const setHeight = function (someNode) {
    do {
        someNode.height = "100px";
    } while (someNode = someNode.parentNode);
}

// Practical example that wraps the assignment in parentheses
const set_height = function (someNode) {
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode));
}

// Practical example that wraps the assignment and tests for 'null'
const heightSetter = function (someNode) {
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode) !== null);
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28

使用 "always" 选项时，此规则的正确代码示例：

🌐 Examples of correct code for this rule with the "always" option:

/*eslint no-cond-assign: ["error", "always"]*/

// Assignment replaced by comparison
let x;
if (x === 0) {
    const b = 1;
}
1
2
3
4
5
6
7

相关规则

• no-extra-parens

版本

此规则是在 ESLint v0.0.9 中引入。

资源

• 规则源码
• 测试源码