no-sequences

禁止逗号运算符

逗号运算符包含多个表达式，其中只需要一个。它从左到右计算每个操作数并返回最后一个操作数的值。然而，这经常掩盖副作用，并且它的使用通常是一个意外。以下是一些序列示例：

var a = (3, 5); // a = 5

a = b += 5, a + b;

while (a = next(), a && a.length);

(0, eval)("doSomething();");

规则详情

此规则禁止使用逗号运算符，但以下情况除外：

• 在 for 语句的初始化或更新部分。
• 默认情况下，如果表达式序列被显式包裹在括号中。可以使用 allowInParentheses 选项删除此异常。

此规则的错误代码示例：

/*eslint no-sequences: "error"*/

foo = doSomething(), val;

0, eval("doSomething();");

do {} while (doSomething(), !!test);

for (; doSomething(), !!test; );

if (doSomething(), !!test);

switch (val = foo(), val) {}

while (val = foo(), val < 42);

with (doSomething(), val) {}

f/g6SKVZdhoBiPVtnee0m+uPEv1T4kMgIaFUpxdtFwzAZHGBqJ5dJxRHxHHP/cP8

/*eslint no-sequences: "error"*/

foo = (doSomething(), val);

(0, eval)("doSomething();");

do {} while ((doSomething(), !!test));

for (i = 0, j = 10; i < j; i++, j--);

if ((doSomething(), !!test));

switch ((val = foo(), val)) {}

while ((val = foo(), val < 42));

with ((doSomething(), val)) {}

关于箭头函数体的注意事项

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ES+1lG+9vSqqs3Yh9hHLd3Bjr9tEVV+jhLxZ0omZuCOgN9o/UiuTzOUh41sYAcBi

/*eslint no-sequences: "error"*/
const foo = (val) => (console.log('bar'), val);

const foo = () => ((bar = 123), 10);

const foo = () => { return (bar = 123), 10 }

7aNllMhFUSBXw3MxV49MWAkzIGpARsuEOaGYzIhZryHFl51wiDC8zbEcfLRplOnb

/*eslint no-sequences: "error"*/
const foo = (val) => ((console.log('bar'), val));

const foo = () => (((bar = 123), 10));

const foo = () => { return ((bar = 123), 10) }

选项

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NWBVOY2Km4YcrxrVhhTHlZARSFirqYkin4SgL8jM5NxOzwZnTOdOU7GT49RV8cVrmgFQ0Ne53tqi8/oCQ09M0njl4PI9qcNczqYQB36TMvTICscyDo1+3G0Lhm61FcFErL9mEVfx3igCHUJ8WOdEG/aEYuYIAaBhlR1op1Rv3qnJVFtkYbBmuqXncXw+a52IC7Smv4xZGwGmZ9q1CQKFHA==

allowInParentheses

gXTXeFewMhKUGG8XamsAXX9FzZtKatkC2q6n9hBCQ86xWRAxllCE47u7VGq4dvHYbQebwXAIK5oGDQtiI1aI1cUHEb85P7yQ5vt/8kntHC3uPv0OeuArUxY5kXOlYDET

/*eslint no-sequences: ["error", { "allowInParentheses": false }]*/

foo = (doSomething(), val);

(0, eval)("doSomething();");

do {} while ((doSomething(), !!test));

for (; (doSomething(), !!test); );

if ((doSomething(), !!test));

switch ((val = foo(), val)) {}

while ((val = foo(), val < 42));

with ((doSomething(), val)) {}

const foo = (val) => ((console.log('bar'), val));

gXTXeFewMhKUGG8XamsAXX9FzZtKatkC2q6n9hBCQ86xWRAxllCE47u7VGq4dvHYbQebwXAIK5oGDQtiI1aI1d0FVb4NCAD9HcpbsQ2I589kY7UCGrzH3uiJXd7zyhcD

/*eslint no-sequences: ["error", { "allowInParentheses": false }]*/

for (i = 0, j = 10; i < j; i++, j--);

何时不使用

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{
    "rules": {
        "no-restricted-syntax": ["error", "SequenceExpression"]
    }
}