require or disallow initialization in variable declarations (init-declarations)

强制或禁止变量声明语句中初始化 (init-declarations)

In JavaScript, variables can be assigned during declaration, or at any point afterwards using an assignment statement. For example, in the following code, foo is initialized during declaration, while bar is initialized later.

在 JavaScript 中，变量可在声明时初始化，或者在赋值语句中初始化。例如，在下面的代码中，foo 在声明时被初始化，而 bar 在之后被初始化。

var foo = 1;
var bar;

if (foo) {
    bar = 1;
} else {
    bar = 2;
}

Rule Details

This rule is aimed at enforcing or eliminating variable initializations during declaration. For example, in the following code, foo is initialized during declaration, while bar is not.

此规则旨在声明的过程中强制或消除变量在声明时进行初始化。例如，在下面的代码，foo 在声明过程中初始化，而 bar 不是。

var foo = 1;
var bar;

bar = 2;

This rule aims to bring consistency to variable initializations and declarations.

这一规则的目的是保持一致的变量初始化和声明。

Options

The rule takes two options:

该规则有两个选项：

1. A string which must be either "always" (the default), to enforce initialization at declaration, or "never" to disallow initialization during declaration. This rule applies to var, let, and const variables, however "never" is ignored for const variables, as unassigned consts generate a parse error.
2. 一个字符串，值为 "always"（默认）强制在声明时进行初始化，或 "never" 禁止在声明时进行初始化。该规则适用于var、let 和const 变量，然而，const 变量会忽略 "never"，因为未赋值的常量（const）会生成一个解析错误。
3. An object that further controls the behavior of this rule. Currently, the only available parameter is ignoreForLoopInit, which indicates if initialization at declaration is allowed in for loops when "never" is set, since it is a very typical use case.
4. 一个对象，进一步控制该规则的行为。目前，唯一可以的参数是 ignoreForLoopInit ，用来表明在设置了 "never" 之后，是否允许在 for 循环中变量声明时进行初始化，这是一个典型的用例。

You can configure the rule as follows:

你可以配置规则如下：

Variables must be initialized at declaration (default)

变量必须在声明时初始化（默认）

{
    "init-declarations": ["error", "always"],
}

Variables must not be initialized at declaration

变量不能在声明时初始化

{
    "init-declarations": ["error", "never"]
}

Variables must not be initialized at declaration, except in for loops, where it is allowed

除了 for 循环外，变量不能在声明时初始化

{
    "init-declarations": ["error", "never", { "ignoreForLoopInit": true }]
}

always

Examples of incorrect code for the default "always" option:

默认选项 "always" 的 错误 代码示例：

/*eslint init-declarations: ["error", "always"]*/
/*eslint-env es6*/

function foo() {
    var bar;
    let baz;
}

Examples of correct code for the default "always" option:

默认选项 "always" 的 正确 代码示例：

/*eslint init-declarations: ["error", "always"]*/
/*eslint-env es6*/

function foo() {
    var bar = 1;
    let baz = 2;
    const qux = 3;
}

never

Examples of incorrect code for the "never" option:

选项 "never" 的 错误 代码示例：

/*eslint init-declarations: ["error", "never"]*/
/*eslint-env es6*/

function foo() {
    var bar = 1;
    let baz = 2;

    for (var i = 0; i < 1; i++) {}
}

Examples of correct code for the "never" option:

选项 "never" 的 正确 代码示例：

/*eslint init-declarations: ["error", "never"]*/
/*eslint-env es6*/

function foo() {
    var bar;
    let baz;
    const buzz = 1;
}

The "never" option ignores const variable initializations.

选项 "never" 忽略 const 变量的初始化。

ignoreForLoopInit

Examples of correct code for the "never", { "ignoreForLoopInit": true } options:

选项 "never", { "ignoreForLoopInit": true } 的 正确 代码示例：

/*eslint init-declarations: ["error", "never", { "ignoreForLoopInit": true }]*/
for (var i = 0; i < 1; i++) {}

When Not To Use It

When you are indifferent as to how your variables are initialized.

如果你不关心变量如何初始化，可以关闭此规则。

Version

This rule was introduced in ESLint 1.0.0-rc-1.

该规则在 ESLint 1.0.0-rc-1 中被引入。

Resources

• Rule source
• Documentation source