Running a scheduled function on Val Town to import Atom feeds into Datasette Cloud#

Val Town is a neat service for hosting short server-side JavaScript programs online - reminiscent of a combination of Glitch and Observable Notebooks.

Today I figured out how to use it to run an hourly task (a “Val”) that fetches data from an Atom feed, parses it and then submits the resulting parsed data to a table running on Datasette Cloud via the Datasette JSON write API.

Configuring secrets in environment variables#

Because this Val needs to be able to call the Datasette Cloud API with an API token, I needed to figure out Val Town secrets. These are pretty straight-forward: you can set multiple environment variables for your account on this page:

https://www.val.town/settings/environment-variables

Those variables are then made available to your Vals through Deno.env.get("VARIABLE_NAME").

Scheduling a Val#

The Val Town logged in homepage looks like this:

Create a val. Options are: Email handler, Scheduled function, HTTP handler, Templates...

Clicking “Scheduled function” creates a new private Val with a random name that looks like this:

coraCicado - Interval - v0, private - runs every 1 hrs - export default async function (interval: Interval) {}

The cog next to “Runs every 1hr” can be used to set a different interval.

Writing the code#

After some experimentation I landed on this as the content of my Val:

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export default async function(interval: Interval) {
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  const { default: Parser } = await import("npm:rss-parser");
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  let parser = new Parser();
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  let feed = await parser.parseURL("https://simonwillison.net/atom/everything/");
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  const token = Deno.env.get("DATASETTE_CLOUD_SIMON_FEED_WRITE");
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  const url = "https://simon.datasette.cloud/data/feed/-/insert";
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  const body = {
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    "rows": feed.items,
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    "replace": true,
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  };
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  const response = await fetch(url, {
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    method: "POST",
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    headers: {
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      "Content-Type": "application/json",
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      "Authorization": `Bearer ${token}`,
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    },
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    body: JSON.stringify(body),
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  });
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  if (response.ok) {
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    const responseData = await response.json();
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    console.log("Response data:", responseData);
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  } else {
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    console.error("Request failed:", response.statusText);
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  }
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}

Any NPM module can be imported directly into a Val using await import("npm:name-of-package")
I used rss-parser to parse the feed - it was the first option I tried and provided exactly what I wanted
As mentioned earlier, Deno.env.get() provides access to configured environment variables
Deno’s fetch() function is modeled on the browser standard
console.log() and console.error() log to a dedicated log for that Val, visible beneath it

The blue “Run” button can be clicked any time to try out the Val. Once I got it working I left it running, and it’s been executing once an hour ever since.