Add `lowlight.registered`

[fengzilong]

In the following case

// register 'js' as alias of `javascript`
lowlight.registerAlias( 'javascript', 'js' )

// I want to know whether `js` is registered
const hasJSLang = lowlight.listLanguages().indexOf( 'js' ) > -1

// `hasJSLang` is `false` here
if ( hasJSLang ) {
  lowlight.highlight( 'js', code )
} else {
  lowlight.highlightAuto( code )
}

lowhight.listLanguages() doesn't include alias, so there is no method exposed to tell us whether an alias is registered

This problem can be solved by exposing lowlight.getLanguage

const hasJSLang = Boolean( lowlight.getLanguage( 'js' ) ) // -> true

BTW, I found someone use highlight.listLanguages to build a Select component in browser, so I decide to send a PR here rather than highlight.js repository

[wooorm]

1. I don’t really see a case for why people need to access to a grammar
2. .getLanguage resolving an alias might be unintuitive?

Would perhaps a registered(aliasOrLanguage): boolean work?

[fengzilong]

It makes sense for me. Already rename to registered and return a boolean type

[joshgoebel]

I'm spoiled by Wren lately but I'd suggest isRegistered. :-)

[fengzilong]

I'm spoiled by Wren lately but I'd suggest isRegistered. :-)

Both is ok for me 😉. @wooorm What's your opinion on the naming?

[wooorm]

@joshgoebel What’s “Wren”?

---

It’s a bit of an unimportant stylistic choice, whether to prefix with is* or has*. I’ve done that before but personally am more in favor of without the prefix. It’s unambiguous enough in my opinion!

[wooorm]

@fengzilong Could you add a test? And docs?

[joshgoebel]

https://wren.io

@wooorm I'm truly spoiled by Ruby where we have registered?... I think isRegistered (to me) has a bit more of that "flavor"...

[fengzilong]

@fengzilong Could you add a test? And docs?

I'll add test & docs soon when I get off work

[fengzilong]

@fengzilong Could you add a test? And docs?

Test and docs added

[fengzilong]

updated

[wooorm]

Thanks @fengzilong! (and @joshgoebel)