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 ==）误键入为赋值运算符（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
}
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在条件语句中使用赋值运算符是有充分理由的。然而，很难判断一个特定的任务是否是故意的。

¥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

此规则不允许在 if、for、while 和 do...while 语句的测试条件中使用模棱两可的赋值运算符。

¥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）仅当赋值括在括号中时才允许在测试条件中进行赋值（例如，允许在 while 或 do...while 循环的测试中重新分配变量）。

  ¥"except-parens" (default) allows assignments in test conditions only if they are enclosed in parentheses (for example, to allow reassigning a variable in the test of a while or do...while loop).

• "always" 不允许在测试条件中进行所有赋值。

  ¥"always" disallows all assignments in test conditions.

except-parens

使用默认 "except-parens" 选项的此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);
}
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使用默认 "except-parens" 选项的此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);
}
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always

使用 "always" 选项的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);
}
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使用 "always" 选项的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;
}
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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