ESLintdisallow variable redeclaration (no-redeclare)
禁止重新声明变量 (no-redeclare)
The "extends": "eslint:recommended" property in a configuration file enables this rule.
配置文件中的 "extends": "eslint:recommended" 属性启用了此规则。
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 true.
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true。
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Object、Array、Number…
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 } 的 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:
在 browser 环境下，选项 {"builtinGlobals": true} 的 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 node 或 commonjs 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。
Related Rules
Version
This rule was introduced in ESLint 0.0.9.
该规则在 ESLint 0.0.9 中被引入。