huh, it appears the vscode does not use typings for markdown-it: https://github.com/Microsoft/vscode/blob/master/extensions/markdown/src/extension.ts

You can make the bottom of the markdown-it.d.ts file this to get it working:

declare module "markdown-it" {
  export = MarkdownIt;
}

@jasongrout Thanks.

I believe what is happening is this:

The original repo had typescript looking for the filename markdown-it.d.ts because the .d.ts file was in the compiler path, i.e., was part of the files that were being compiled already by the compiler. However, in our case, the typings files are not included in the list of files compiled in with the compiler, but instead are explicitly included in the src/typings.d.ts file. It would be hard to switch because tsconfig lacks globbing support in the files parameter (coming in 2.0, see microsoft/TypeScript#8841).

So instead of relying on ts to find a 'markdown-it.d.ts' file, we explicitly declare the module in the file which we are including.

Turns out we do need to have some delay for updating markdown during model changes. Mathjax rendering is done for every keypress, which can really slow things down a lot.

#445 should help out with reducing redundant renders.

Makes sense. I just merged #445.

The most recent commits allow you to render markdown documents with either marked or markdown-it. This should help with comparing how documents are rendered.
MarkdownWidget = rendered with marked
MarkdownItWidget = rendered with markdown-it

What is the status of this PR?

Thinking a bit more about how we render markdown in the browser. While I am in favor of using CommonMark, I don't think we should do that only in JupyterLab as it may break notebooks. We would want to change this in both JLab and the classic notebook in a parallel major release. I am going to work on fixing the marked support in JupyterLab for now.

Because of these factors, I am going to close this PR. We can revisit later as we get closer to transitioning to CommonMark in all of our apps.