Top HN post alerts

Overview

Let’s set up a script that alerts us every hour of new posts on the front page of Hacker News that have exceeded a certain point threshold. Here’s how we’ll tackle it:

Write the script to fetch all front page posts with a minimum upvote score
Set up a notification to be sent to Discord whenever a new post is found
Configure the schedule so that it “remembers” which posts have already been sent through

Just show me the code

See the finished code on Replit.You can even use the Replit URL to run your job, as long as the Repl is running. Make sure to replace YOUR_DISCORD_WEBHOOK_URL with your Discord webhook URL, and then you can run the following in your terminal:

# This assumes your API key is set in the current env
# BOOPER_API_KEY=sk_...

curl --location --request POST 'https://scheduler.booper.dev/api/jobs' \
--header "Content-Type: application/json" \
--header "Authorization: Bearer $BOOPER_API_KEY" \
--data-raw '{
    "method": "post",
    "url": "https://hn.reichertjalex.repl.co/api/run",
    "body": {
      "min": 200,
      "webhook": YOUR_DISCORD_WEBHOOK_URL,
      "exclude": "$previous.sent"
    },
    "repeat_every": [1, "hour"]
}'

# Assumes your webhook URL is set in the current env:
# DISCORD_WEBHOOK_URL=https://discord.com/api/webhooks/...

npx @booper/cli run \
  POST https://hn.reichertjalex.repl.co/api/run \
  --data 'min=200' \
  --data "webhook=$DISCORD_WEBHOOK_URL" \
  --data 'exclude=$previous.sent' \
  --every '1 hour'

Fetching top stories from HN

We’ll use the Hacker News API endpoints to fetch the top page stories. Here’s what that function might look like:

const get = async (url) => fetch(url).then((r) => r.json());

const fetchStories = async ({ pages = 1, min = 100, exclude = [] } = {}) => {
  const storyIds = await get(
    `https://hacker-news.firebaseio.com/v0/topstories.json`
  );

  return Promise.all(
    storyIds
      // Filter out posts we've already seen
      .filter((id) => !exclude.includes(id))
      // Limit to the first page (30 posts per page)
      .slice(0, pages * 30)
      .map(async (id) => {
        const story = await get(
          `https://hacker-news.firebaseio.com/v0/item/${id}.json`
        );

        return story;
      })
  );
};

const get = async (url: string) => fetch(url).then((r) => r.json());

const fetchStories = async ({
  pages = 1,
  min = 100,
  exclude = [],
}: {
  pages?: number;
  min?: number;
  exclude?: number[];
}) => {
  const storyIds = await get(
    `https://hacker-news.firebaseio.com/v0/topstories.json`
  );

  return Promise.all(
    storyIds
      // Filter out posts we've already seen
      .filter((id: number) => !exclude.includes(id))
      // Limit to the first page (30 posts per page)
      .slice(0, pages * 30)
      .map(async (id: number) => {
        const story = await get(
          `https://hacker-news.firebaseio.com/v0/item/${id}.json`
        );

        return story;
      })
  );
};

It’s basically an N+1 query, but no big deal. If we limit the results to the first page (i.e. the first 30 posts), the request is generally fast enough.

View example output of HN posts

Here’s an example of what the output looks like:

{
  "stories": [
    {
      "title": "Get a cable modem, go to jail (1999)",
      "url": "http://telecom.csail.mit.edu/judy-sammel.html",
      "score": 447
    },
    {
      "title": "Writing a C compiler in 500 lines of Python",
      "url": "https://vgel.me/posts/c500/",
      "score": 432
    },
    {
      "title": "Emacs Bedrock: A minimal Emacs starter kit",
      "url": "https://sr.ht/~ashton314/emacs-bedrock/",
      "score": 214
    }
    // ...
  ]
}

Triggering a Discord alert when new posts are found

First, let’s define two helper functions:

format: formats story data into Discord markdown
notify: sends an alert to Discord via webhook URL

const format = (results) => {
  return results
    .map((p) => `[${p.score} points] [${p.title}](${p.url})`)
    .join("\n");
};

const notify = async (content, webhook = process.env.DISCORD_WEBHOOK_URL) => {
  return fetch(webhook, {
    headers: { "content-type": "application/json" },
    method: "POST",
    body: JSON.stringify({ content }),
  });
};

type Post = { id: number; score: number; title: string; url: string };

const format = (results: Post[]) => {
  return results
    .map((p) => `[${p.score} points] [${p.title}](${p.url})`)
    .join("\n");
};

const notify = async (content: string, webhook = DISCORD_WEBHOOK_URL) => {
  return fetch(webhook, {
    headers: { "content-type": "application/json" },
    method: "POST",
    body: JSON.stringify({ content }),
  });
};

Now, the simplest thing we can do is just send an alert to Discord whenever we find posts that meet the minimum score requirement set in the request body. Here we handle that in a NextJS API endpoint:

export default async function handler(req, res) {
  const { min = 100, pages = 1 } = req.body;
  const stories = await fetchStories({ pages });
  // After we fetch the stories, we filter out the ones that
  // don't have the minimum score specified in the request body
  const results = stories.filter((s) => s.score >= min);

  if (results.length > 0) {
    // Send notification to Discord using the helpers defined above
    await notify(format(results));
  }

  return res.status(200).json({ results });
}

import express from "express";

const app = express();

app.use(express.json());

app.post("/api/hn", async (req, res) => {
  const { min = 100, pages = 1 } = req.body;
  const stories = await fetchStories({ pages });
  // After we fetch the stories, we filter out the ones that
  // don't have the minimum score specified in the request body
  const results = stories.filter((s) => s.score >= min);

  if (results.length > 0) {
    // Send notification to Discord using the helpers defined above
    await notify(format(results));
  }

  return res.status(200).json({ results });
});

app.listen(process.env.PORT || 3000, () => console.log("Server initialized!"));

This is fine if we run the script every hour or two, and don’t mind seeing repeated links. But what if we want to avoid sending duplicates?

Keeping track of alert history

There are two ways we can keep track of which posts have been sent out already. When you create a job on a schedule, the scheduler will pass in some metadata into the body of each request. Included in that metadata is the response from the previous run, which can be seen at req.body.$previous.

Example using the `$previous` metadata

Let’s modify the API handler to take advantage of the $previous data:

export default async function handler(req, res) {
  const { min = 100, pages = 1 } = req.body;
  // Add this line! 👇
  const exclude = req.body.$previous?.sent || [];
  // And then pass in the `exclude` parameter to exclude
  // previously sent posts from the results of `fetchStories`
  const stories = await fetchStories({ pages, exclude });
  const results = stories.filter((s) => s.score >= min);

  if (results.length > 0) {
    await notify(format(results));
  }

  return res.status(200).json({
    // And modify the response to return all the IDs of sent posts,
    // including the previously sent posts (from `exclude`) 👇
    sent: [...exclude, ...results.map((s) => s.id)],
  });
}

If we want, we can also clean this up a bit by taking advantage of dynamic values in our job schedule configuration. When we set the request body for our job, we can write it like this:

{
  // Set the minimum score requirement to 200 points
  "min": 200,
  // Pass in `req.body.$previous?.sent` as `req.body.exclude`
  "exclude": "$previous.sent"
}

If we do this, we can change the line above from this:

const exclude = req.body.$previous?.sent || [];

To this:

const exclude = req.body.exclude || [];

Now, assuming you’ve deployed your API endpoint to https://yourdomain.com/api/hn, you can create your scheduled job by running the following script in your terminal with your BOOPER_API_KEY set, and the url modified to the appropriate domain:

# This assumes your API key is set in the current env
# BOOPER_API_KEY=sk_...

curl --location --request POST 'https://scheduler.booper.dev/api/jobs' \
--header "Content-Type: application/json" \
--header "Authorization: Bearer $BOOPER_API_KEY" \
--data-raw '{
    "method": "post",
    "url": "https://yourdomain.com/api/hn",
    "body": {"min": 200, "exclude": "$previous.sent"},
    "repeat_every": [1, "hour"]
}'

npx @booper/cli run \
  POST https://yourdomain.com/api/hn \
  --data 'min=200' \
  --data 'exclude=$previous.sent' \
  --every '1 hour'

Also included in the metadata is the schedule’s state, which can be accessed at req.body.$state and set or updated in the response.

Example using the schedule `$state`

Let’s modify the API handler to take advantage of $state:

export default async function handler(req, res) {
  const { min = 100, pages = 1 } = req.body;
  // Add this line! 👇
  const exclude = req.body.$state?.sent || [];
  // And then pass in the `exclude` parameter to exclude
  // previously sent posts from the results of `fetchStories`
  const stories = await fetchStories({ pages, exclude });
  const results = stories.filter((s) => s.score >= min);

  if (results.length > 0) {
    await notify(format(results));
  }

  return res.status(200).json({
    $set: {
      sent: [...exclude, ...results.map((s) => s.id)],
    },
  });
}

This may look similar to what we did above when using the $previous metadata, but there is one key difference: while $previous data is ephemeral, the schedule’s $state is stored in the database. This means that if a schedule is paused and then restarted again, the $previous data will be lost, but $state will be persisted.Once again, we can clean this up a bit by taking advantage of dynamic values in our job schedule configuration. When we set the request body for our job, we can write it like this:

{
  // Set the minimum score requirement to 200 points
  "min": 200,
  // Pass in `req.body.$state?.sent` as `req.body.exclude`
  "exclude": "$state.sent"
}

If we do this, we can change the line above from this:

const exclude = req.body.$state?.sent || [];

To this:

const exclude = req.body.exclude || [];

# This assumes your API key is set in the current env
# BOOPER_API_KEY=sk_...

curl --location --request POST 'https://scheduler.booper.dev/api/jobs' \
--header "Content-Type: application/json" \
--header "Authorization: Bearer $BOOPER_API_KEY" \
--data-raw '{
    "method": "post",
    "url": "https://yourdomain.com/api/hn",
    "body": {"min": 200, "exclude": "$state.sent"},
    "repeat_every": [1, "hour"]
}'

npx @booper/cli run \
  POST https://yourdomain.com/api/hn \
  --data 'min=200' \
  --data 'exclude=$state.sent' \
  --every '1 hour'

Documentation

API Reference

Jobs

Schedules

Logs

Miscellaneous

Top HN post alerts

Overview

Fetching top stories from HN

Triggering a Discord alert when new posts are found

Keeping track of alert history

​Overview

​Fetching top stories from HN

​Triggering a Discord alert when new posts are found

​Keeping track of alert history

Overview

Fetching top stories from HN

Triggering a Discord alert when new posts are found

Keeping track of alert history