What’s the point of (?!\*)?

[valtlai]

I’m trying to understand the Prism source code. What’s the point of (?!\*) in the following line:

var lang = /\blang(?:uage)?-(?!\*)(\w+)\b/i;

I know it’s a negative lookahead. In this regex it means that an asterisk doesn’t follow the hyphen.

But where is it needed?

[kylekatarnls]

HI, foo(?!bar) mean "take foo if it's not followed with bar". * is the * symbol. So it takes - if it's not followed with * then a word. So lang-php, language-html, but not lang-*php.

[valtlai]

But how that regex differs from one without (?!\*)?

/\blang(?:uage)?-(?!\*)(\w+)\b/i.test('lang-*php');  // returns `false`
/\blang(?:uage)?-(\w+)\b/i.test('lang-*php');  // returns `false` too!

[kylekatarnls]

Ho, indeed, \w exclude *, you're right it's redundant. What's the line and file? With them we could know who wrote this and ask him/her if there is a reason.

[valtlai]

It’s here: /components/prism-core.js:18

Added in cfaf681

[kylekatarnls]

It seems @LeaVerou added this piece of the RegExp specifically: cfaf681
But there are no differences when I test with examples.html classes.

[LeaVerou]

Yeah, I have no idea why I added that, since as you pointed out, \w doesn't include * anyway. It can be safely removed.

[valtlai]

Thanks!