enh(parser) post-highlightBlock callbacks via plugin

[joshgoebel]

• add tests

---

First pass at simple plugin API to allow things like:

    hljs.addPlugin( {
      "after:highlightBlock": ({block, result}) => {
        // move the language from the result into the dataset
        block.dataset.language = result.language }
    })

I realize I need to document the plugin API itself and the callbacks, but how does this look at a high level? We'd also support classes for more complex plugins:

  class DataLanguagePlugin {
    constructor(options) {
      self.prefix = options.dataPrefix;
    }

    afterHighlightBlock({block, result}) {
      // ...
    }
  }

  hljs.addPlugin(DataLanguagePlugin, { dataPrefix: "hljs"})

Passing a class being the preferred way for more complex things, and the object based approach serves for one-liners to make them easy to whip up.

[egor-rogov]

I haven't yet tried it, just had a look, but generally I like it. See a couple of comments in code.

[joshgoebel]

@egor-rogov How you feeling about this in general? Can I polish it up for merging? (which requires building out the class functionality, writing some tests, better docs.)

I'll ping you again for a final review, but I wanted to make sure you're cool with the naming before I put more effort into this.

[egor-rogov]

How you feeling about this in general? Can I polish it up for merging? (which requires building out the class functionality, writing some tests, better docs.)

Definitely yes.
My only concern is events-functions mapping. I feel it's important to use only events names in plugin code.

[joshgoebel]

Don't we resolve that by just saying "always use the event names", as suggested above:

  class DataLanguagePlugin {
    constructor(options) {
      this.prefix = options.dataPrefix;
    }

    'after:highlightBlock'({block, result}) {
      // ...
    }
  }

[egor-rogov]

Don't we resolve that by just saying "always use the event names"

We do.

[joshgoebel]

I want to review the tests here and perhaps add a few more but is this otherwise good to merge?

[joshgoebel]

@egor-rogov Ping?

[egor-rogov]

Sorry for delay.
I like it!