max-lines-per-function

在函数中强制执行最大代码行数

有些人认为大型函数是一种代码味道。大型函数往往会做很多事情，并且很难跟踪正在发生的事情。许多编码风格指南规定了函数可以包含的行数限制。这条规则可以帮助强制执行这种风格。

¥Some people consider large functions a code smell. Large functions tend to do a lot of things and can make it hard following what’s going on. Many coding style guides dictate a limit of the number of lines that a function can comprise of. This rule can help enforce that style.

规则详情

¥Rule Details

此规则强制每个函数的最大行数，以帮助可维护性并降低复杂性。

¥This rule enforces a maximum number of lines per function, in order to aid in maintainability and reduce complexity.

为什么不使用 max-statements 或其他复杂度测量规则呢？

¥Why not use max-statements or other complexity measurement rules instead?

为了便于阅读，像下面的示例这样的嵌套长方法链通常被分成单独的行：

¥Nested long method chains like the below example are often broken onto separate lines for readability:

function() {
    return m("div", [
        m("table", {className: "table table-striped latest-data"}, [
            m("tbody",
                data.map(function(db) {
                    return m("tr", {key: db.dbname}, [
                        m("td", {className: "dbname"}, db.dbname),
                        m("td", {className: "query-count"},  [
                            m("span", {className: db.lastSample.countClassName}, db.lastSample.nbQueries)
                        ])
                    ])
                })
            )
        ])
    ])
}
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• 尽管有 16 行代码，max-statements 只会将此报告为 1 条语句。

  ¥max-statements will only report this as 1 statement, despite being 16 lines of code.

• complexity 只会报告复杂度为 1

  ¥complexity will only report a complexity of 1

• max-nested-callbacks 只会报 1

  ¥max-nested-callbacks will only report 1

• max-depth 将报告深度为 0

  ¥max-depth will report a depth of 0

选项

¥Options

此规则具有以下可使用对象指定的选项：

¥This rule has the following options that can be specified using an object:

• "max"（默认 50）强制函数中的最大行数。

  ¥"max" (default 50) enforces a maximum number of lines in a function.

• "skipBlankLines"（默认 false）忽略纯粹由空格组成的行。

  ¥"skipBlankLines" (default false) ignore lines made up purely of whitespace.

• "skipComments"（默认 false）忽略仅包含注释的行。

  ¥"skipComments" (default false) ignore lines containing just comments.

• "IIFEs"（默认 false）包括 IIFE 中包含的任何代码。

  ¥"IIFEs" (default false) include any code included in IIFEs.

或者，你可以为 max 选项指定一个整数：

¥Alternatively, you may specify a single integer for the max option:

"max-lines-per-function": ["error", 20]
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相当于

¥is equivalent to

"max-lines-per-function": ["error", { "max": 20 }]
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code

具有特定最大值的此规则的错误代码示例：

¥Examples of incorrect code for this rule with a particular max value:

/*eslint max-lines-per-function: ["error", 2]*/
function foo() {
    var x = 0;
}
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/*eslint max-lines-per-function: ["error", 3]*/
function foo() {
    // a comment
    var x = 0;
}
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/*eslint max-lines-per-function: ["error", 4]*/
function foo() {
    // a comment followed by a blank line

    var x = 0;
}
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具有特定最大值的此规则的正确代码示例：

¥Examples of correct code for this rule with a particular max value:

/*eslint max-lines-per-function: ["error", 3]*/
function foo() {
    var x = 0;
}
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/*eslint max-lines-per-function: ["error", 4]*/
function foo() {
    // a comment
    var x = 0;
}
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/*eslint max-lines-per-function: ["error", 5]*/
function foo() {
    // a comment followed by a blank line

    var x = 0;
}
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skipBlankLines

使用 { "skipBlankLines": true } 选项的此规则的错误代码示例：

¥Examples of incorrect code for this rule with the { "skipBlankLines": true } option:

/*eslint max-lines-per-function: ["error", {"max": 2, "skipBlankLines": true}]*/
function foo() {

    var x = 0;
}
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使用 { "skipBlankLines": true } 选项的此规则的正确代码示例：

¥Examples of correct code for this rule with the { "skipBlankLines": true } option:

/*eslint max-lines-per-function: ["error", {"max": 3, "skipBlankLines": true}]*/
function foo() {

    var x = 0;
}
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skipComments

使用 { "skipComments": true } 选项的此规则的错误代码示例：

¥Examples of incorrect code for this rule with the { "skipComments": true } option:

/*eslint max-lines-per-function: ["error", {"max": 2, "skipComments": true}]*/
function foo() {
    // a comment
    var x = 0;
}
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使用 { "skipComments": true } 选项的此规则的正确代码示例：

¥Examples of correct code for this rule with the { "skipComments": true } option:

/*eslint max-lines-per-function: ["error", {"max": 3, "skipComments": true}]*/
function foo() {
    // a comment
    var x = 0;
}
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IIFEs

使用 { "IIFEs": true } 选项的此规则的错误代码示例：

¥Examples of incorrect code for this rule with the { "IIFEs": true } option:

/*eslint max-lines-per-function: ["error", {"max": 2, "IIFEs": true}]*/
(function(){
    var x = 0;
}());

(() => {
    var x = 0;
})();
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使用 { "IIFEs": true } 选项的此规则的正确代码示例：

¥Examples of correct code for this rule with the { "IIFEs": true } option:

/*eslint max-lines-per-function: ["error", {"max": 3, "IIFEs": true}]*/
(function(){
    var x = 0;
}());

(() => {
    var x = 0;
})();
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何时不使用

¥When Not To Use It

如果你不关心函数中的行数，可以关闭此规则。

¥You can turn this rule off if you are not concerned with the number of lines in your functions.

相关规则

• complexity
• max-depth
• max-lines
• max-nested-callbacks
• max-params
• max-statements
• max-statements-per-line

版本

此规则是在 ESLint v5.0.0 中引入。

资源

• 规则源码
• 测试源码