Disallow Use of the Comma Operator (no-sequences)

不允许使用逗号操作符 (no-sequences)

The comma operator includes multiple expressions where only one is expected. It evaluates each operand from left to right and returns the value of the last operand. However, this frequently obscures side effects, and its use is often an accident. Here are some examples of sequences:

逗号操作符包含多个表达式，其中只有一个是可使用的。它从左到右计算每一个操作数并且返回最后一个操作数的值。然而，这往往掩盖了它的副作用，它的使用经常会发生事故。例如：

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

a = b += 5, a + b;

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

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

Rule Details

This rule forbids the use of the comma operator, with the following exceptions:

此规则禁止逗号操作符的使用，以下情况除外：

Examples of incorrect code for this rule:

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) {}

Examples of correct code for this rule:

正确 代码示例：

/*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)) {}

When Not To Use It

Disable this rule if sequence expressions with the comma operator are acceptable. Another case is where you might want to report all usages of the comma operator, even if they are wrapped in parentheses or in a for loop. You can achieve this using rule no-restricted-syntax:

如果逗号操作符在有序的表达式中使用是可接受的，禁用此规则。另一种情况是，你可能希望报告逗号操作符的所有用法，即使它们是用在括号或for 循环中。你可以使用 no-restricted-syntax 规则实现此功能：

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

Version

This rule was introduced in ESLint 0.5.1.

该规则在 ESLint 0.5.1 中被引入。

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