disallow sparse arrays (no-sparse-arrays)

禁用稀疏数组

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。

Sparse arrays contain empty slots, most frequently due to multiple commas being used in an array literal, such as:

稀疏数组包括很多空位置，经常是由于在数组字面量中使用多个逗号造成的，例如：

var items = [,,];

While the items array in this example has a length of 2, there are actually no values in items[0] or items[1]. The fact that the array literal is valid with only commas inside, coupled with the length being set and actual item values not being set, make sparse arrays confusing for many developers. Consider the following:

在这个例子中，item 数组的 length 为 2，实际上，items[0] 或 items[1]并没有值。数组中只有逗号是有效的，再加上 length 被设置，没有实际的值被设置，这些情况让很多开发者对稀疏数组感到困惑。考虑下面的情况：

var colors = [ "red",, "blue" ];

In this example, the colors array has a length of 3. But did the developer intend for there to be an empty spot in the middle of the array? Or is it a typo?

在这个例子中，colors 数值的 length 是 3。但是否是开发者想让数组中间出现一个空元素？或者只是一个书写错误？

The confusion around sparse arrays defined in this manner is enough that it’s recommended to avoid using them unless you are certain that they are useful in your code.

稀疏数组的定义方式造成了很大的困惑，建议避免使用它们，除非你确定它们在你的代码中很有用。

Rule Details

This rule disallows sparse array literals which have “holes” where commas are not preceded by elements. It does not apply to a trailing comma following the last element.

该规则禁止使用稀疏数组，也就是逗号之前没有任何元素的数组。该规则不适用于紧随最后一个元素的拖尾逗号的情况。

Examples of incorrect code for this rule:

错误 代码示例：

/*eslint no-sparse-arrays: "error"*/

var items = [,];
var colors = [ "red",, "blue" ];

Examples of correct code for this rule:

正确 代码示例：

/*eslint no-sparse-arrays: "error"*/

var items = [];
var items = new Array(23);

// trailing comma (after the last element) is not a problem
var colors = [ "red", "blue", ];

When Not To Use It

If you want to use sparse arrays, then it is safe to disable this rule.

如果你想使用稀疏数组，可以关闭此规则。

Further Reading

Version

This rule was introduced in ESLint 0.4.0.

该规则在 ESLint 0.4.0 中被引入。

Resources