disallow variable redeclaration (no-redeclare)

禁止重新声明变量 (no-redeclare)

In JavaScript, it’s possible to redeclare the same variable name using var. This can lead to confusion as to where the variable is actually declared and initialized.

在 JavaScript 中,使用 var 可以对同一个变量再次声明。这会使变量实际声明和定义的位置混乱不堪。

Rule Details

This rule is aimed at eliminating variables that have multiple declarations in the same scope.

此规则目旨在消除同一作用域中多次声明同一变量。

Examples of incorrect code for this rule:

错误 代码示例:

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

var a = 3;
var a = 10;

Examples of correct code for this rule:

正确 代码示例:

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

var a = 3;
// ...
a = 10;

Options

This rule takes one optional argument, an object with a boolean property "builtinGlobals". It defaults to false.

该规则有一个选项参数,是个对象,该对象有个布尔属性为 "builtinGlobals"。默认为false

If set to true, this rule also checks redeclaration of built-in globals, such as Object, Array, Number

如果设置为 true,该规则也会检查全局内建对象,比如ObjectArrayNumber

builtinGlobals

The "builtinGlobals" option will check for redeclaration of built-in globals in global scope.

"builtinGlobals" 选项将会在全局范围检查被重新声明的内置全局变量。

Examples of incorrect code for the { "builtinGlobals": true } option:

选项 { "builtinGlobals": true }错误 代码示例:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/

var Object = 0;

Examples of incorrect code for the { "builtinGlobals": true } option and the browser environment:

browser 环境下,选项 {"builtinGlobals": true}错误 代码示例:

/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/

var top = 0;

The browser environment has many built-in global variables (for example, top). Some of built-in global variables cannot be redeclared.

browser 环境有很多内建的全局变量(例如,top)。一些内建的全局变量不能被重新声明。

Note that when using the node or commonjs environments (or ecmaFeatures.globalReturn, if using the default parser), the top scope of a program is not actually the global scope, but rather a “module” scope. When this is the case, declaring a variable named after a builtin global is not a redeclaration, but rather a shadowing of the global variable. In that case, the no-shadow rule with the "builtinGlobals" option should be used.

注意,当使用 nodecommonjs 环境 (或 ecmaFeatures.globalReturn,如果使用默认解析器)时,则程序的最大作用域不是实际的全局作用域,而是一个模块作用域。当出现这种情况时,声明一个以内置的全局变量命令的变量,不算是重声明,只是遮蔽了全局变量。在这种情况下,应该使用 no-shadow 规则的 "builtinGlobals" 选项。

Version

This rule was introduced in ESLint 0.0.9.

该规则在 ESLint 0.0.9 中被引入。

Resources