javascript - 为什么 JSLint 告诉我使用“=== undefined”而不是“typeof ... === 'undefined'”？

Question

我编写了以下代码：

showTitles = (typeof showTitles !== 'undefined') ? showTitles : 'Y';
showSelectGroup = (typeof showSelectGroup !== 'undefined') ? showSelectGroup : 'Y';

但是 JSLint 说：

警告 3 JS Lint：意外的“typeof”。使用 '===' 直接与 undefined 进行比较。

我应该如何更改我的代码？

Answer 1

Probably by using

showTitles = (showTitles === undefined) ? 'Y' : showTitles;
showSelectGroup = (showSelectGroup === undefined) ? 'Y' : showSelectGroup;

jslint has no issues with that (assuming showTitles and showSelectGroup are declared with var)

However, I'd write it as

var showTitles = showTitles || 'Y';
var showSelectGroup = showSelectGroup || 'Y';

Answer 2

Note that whether this is best practice in general is debatable, but if you want to make it work with JSLint, you could do this

showTitles = (showTitles !== undefined) ? showTitles : 'Y';

Answer 3

此消息反映了最新的最佳实践。从 ES5 严格模式开始， 的全局值undefined 不再可以更改，直接比较代码更简单，速度更快。简而言之，JSLint 了解这一切，并为您提供了很好的建议。

在这种情况下，更改typeof showTitles !== 'undefined'为showTitles === undefined。