[skybrian]

With regard to code edits (rather than UI reactivity), this looks similar to how many web development environments watch the file system for changes and then rebuild and reload the page. Is there more to it?

How are syntax errors reported? Is there support for TypeScript syntax and type-checking? Can a page partially run that has errors in some JavaScript snippets, like a notebook with errors in some cells?

In the examples, there is a “view source” link that goes to GitHub. Understanding the code involves finding the Markdown file and then going back and forth between the published page and the Markdown file, which hopefully correspond to the same version.

It seems like the thing that’s lost compared to notebooks is letting the user see and edit the code in the browser. But I suppose that’s a niche use case for coding tutorials. Not everything needs to be a notebook.

Even so, better built-in “view source” support might be nice, even if it doesn’t allow editing. It doesn’t have to be as prominent as it is in a notebook to be useful.

[mbostock]

You can read about our reactive runtime here (it’s the same as Observable notebooks even though Framework uses vanilla JavaScript syntax):

https://observablehq.com/@observablehq/how-observable-runs

And the source is here:

https://github.com/observablehq/runtime

The “trick” is to structure all code as reactive variables (or nodes, defined as pure functions) within a dataflow graph. So if you replace one variable (by replacing a function with a new import), you then have to recompute any downstream variables that depend on the replaced variable, while cleaning up old variables and updating the display.

Invalid syntax doesn’t prevent other code blocks from running (though if it means a variable is then undefined, that might cause downstream errors). Syntax errors are displayed in the page, and also in the console for the running preview server. We’d like to improve the error display in the console to show more context around where the error occurred, since unlike notebooks the code isn’t immediately adjacent to the output.

We don’t support TypeScript yet, but there’s a PR (https://github.com/observablehq/framework/pull/129) and we are interested in stronger validation at build time to catch more errors.

And yes, we’re making different tradeoffs, optimizing for data apps and dashboards (more polished presentation) rather than ad hoc exploration in notebooks. So it’s more work to find and edit the code, but conversely it’s a more careful, deliberate process that allows code review, unit tests, continuous integration, etc. And we think that’s appropriate for data apps that are depended on by many people.

But still, a view source link back to your source control would be nice, yes!