no-cond-assign

禁止条件表达式中的赋值运算符

配置文件中的 "extends": "eslint:recommended" 属性启用了该规则

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：

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

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。

规则详情

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。

选项

此规则有一个字符串选项：

• "except-parens"（默认）仅在括号括起来时才允许在测试条件中赋值（例如，允许在 while 或 do...while 循环的测试中重新分配变量）
• "always" 不允许在测试条件下进行所有分配

except-parens

此规则使用默认 "except-parens" 选项的错误代码示例：

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

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

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

此规则使用默认 "except-parens" 选项的正确代码示例：

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

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

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

// Practical example that wraps the assignment and tests for 'null'
function setHeight(someNode) {
    "use strict";
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode) !== null);
}

always

此规则使用 "always" 选项的错误代码示例：

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

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

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

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

// Practical example that wraps the assignment and tests for 'null'
function setHeight(someNode) {
    "use strict";
    do {
        someNode.height = "100px";
    } while ((someNode = someNode.parentNode) !== null);
}

此规则使用 "always" 选项的正确代码示例：

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

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