js-a11y/lang not recognizing script subtag

[imtsuki]

According to the documentation for lang attribute on MDN, a valid HTML lang attribute is composed of three parts:

language-[script]-[region]

where the script subtag defines the writing system used for the language, and is always 4 characters long, with the first letter capitalized. This subtag is particularly useful as there are two different writing systems in Chinese: simplified (Hans) and traditional (Hant).

For example, I can have each of the following valid lang attributes:

• zh-CN
• zh-Hant
• zh-Hans-CN

But now the js-a11y/lang rule is rejecting the last two.

Reference:

• lang - HTML: Hypertext Markup Language | MDN

[imtsuki]

I did some investigation. There are actually three languages defined here:

https://github.com/evcohen/eslint-plugin-jsx-a11y/blob/7bcea2006f1d79b399e4aaec82e9cbbbe6ef8cc4/src/util/attributes/ISO.json#L262-L264

But the indexOf('-') here accidentally breaks the last two pairs, which causes the problem:

https://github.com/evcohen/eslint-plugin-jsx-a11y/blob/7bcea2006f1d79b399e4aaec82e9cbbbe6ef8cc4/src/rules/lang.js#L54-L56

[ljharb]

ah, maybe it should be lastIndexOf? or something more precise :-) want to make a PR?