require `let` or `const` instead of `var` (no-var)

要求使用 `let` 或 `const` 而不是 `var`

The --fix option on the command line can automatically fix some of the problems reported by this rule.

命令行中的 --fix 选项可以自动修复一些该规则报告的问题。

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

ECMAScript 6 允许程序员使用 let 和 const 关键字在块级作用域而非函数作用域下声明变量。块级作用域在很多其他编程语言中很普遍，能帮助程序员避免错误，例如：

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

该规则旨在阻止 var 的使用，推荐使用 const 或 let。

Examples

Examples of incorrect code for this rule:

错误代码示例：

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

正确代码示例：

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly.

除了非 ES6 环境外，那些现有 Javascript 项目开始在他们的代码库中引入 ES6 的，如果从 var 迁移到 let 代价高的话，可能并不适用于此规则。

Version

This rule was introduced in ESLint 0.12.0.

该规则在 ESLint 0.12.0 中被引入。

require let or const instead of var (no-var)