I've been building Finterm, a financial terminal
that runs entirely in a browser tab, on Cloudflare
Workers via @opennextjs/cloudflare. The promise
is the obvious one — global edge runtime,
near-zero cold starts, pay-per-request pricing.
The catch is that Workers don't run Node.js. Every
package in your dependency tree has to work in
the Workers runtime, and a surprising number of
common ones don't.

This is a rough log of what I had to rip out and
what I replaced it with, plus a couple of patterns
that turned out to be necessary on Workers but
irrelevant on Node.

## bcrypt → Argon2id via @noble/hashes

bcryptjs reaches for crypto.randomBytes and a
few other Node primitives that aren't polyfilled
in Workers. Argon2id is the modern alternative
anyway, and @noble/hashes exposes a pure-JS
implementation that runs anywhere and lines up
with current OWASP guidance. The migration was a
one-line change in the password hasher plus a
re-hash on next login.

## cheerio / jsdom / parse5 → htmlparser2

For the news reader I needed to extract article
bodies from arbitrary HTML. cheerio pulls in
parse5, which doesn't run on Workers, and
jsdom is even further away from compatibility.
htmlparser2 is SAX-style streaming and pure JS,
so it runs anywhere — but you have to walk the
events yourself rather than querying a tree. Worth
it for the runtime portability.

## The Yahoo Finance crumb handshake

Not a Workers issue specifically, but I hit it
harder because of Workers. Yahoo's quoteSummary,
options, and profile endpoints require a session
cookie and a crumb token bound to that session.
The dance: first you GET https://fc.yahoo.com/,
which returns 404 with Set-Cookie for A1 and A3;
then you GET /v1/test/getcrumb with those
cookies, which returns the crumb as plain text;
then every gated request needs that cookie plus
&crumb=... appended to the URL.

  const seed = await fetch('https://fc.yahoo.com/',
  { headers: BROWSERY });
  const cookie = seed.headers.getSetCookie()
    .map(c => c.split(';')[0])
    .filter(c => c.startsWith('A1=') ||
  c.startsWith('A3=') || c.startsWith('A1S='))
    .join('; ');
  const crumbRes = await fetch('https://query1.finan
  ce.yahoo.com/v1/test/getcrumb', {
    headers: { ...BROWSERY, Cookie: cookie },
  });
  const crumb = (await crumbRes.text()).trim();

A few gotchas. The getcrumb endpoint returns
text/plain, not JSON, so you can't send an
Accept: application/json header — it'll 406. The
User-Agent has to look browsery; a plain
curl/8.x or your fetch library's default gets
rate-limited fast. The cookie and crumb stay valid
for roughly thirty minutes, after which you
re-handshake. I cache the pair per-isolate and
refresh on the first 401.

## Single outbound gateway

Workers isolates are short-lived but they do
persist module state across requests on a single
isolate, which makes the obvious caching patterns
work better than on a per-request serverless
model.

Every upstream HTTP call in the app goes through
one route — /api/data/[...path]. The route looks
up the endpoint by path, runs the provider
function, attaches Cache-Control: s-maxage=N,
stale-while-revalidate=86400, and lets the
Cloudflare edge cache do the heavy lifting. A
four-tier per-IP rate limiter only fires on cache
misses, so a popular ticker can be served to
thousands of users without ever hitting Yahoo or
SEC again that minute.

This pattern also gave me a single chokepoint for
an SSRF guard, so user-supplied paths can't reach
back into Cloudflare's metadata service or some
internal hostname.

## Pop-outs that share React state

Off the Workers topic but a fun one. Each window
in the dashboard has a popout button. It calls
window.open('/popout.html'), then React-renders
the same component switch into the popout's
document. The popout writes back to the parent's
workspace state through a callback, so edits
round-trip in real time.

Two non-obvious things had to change in the
window-body components. Any addEventListener or
matchMedia has to be bound to the popout's own
window (I expose this through a
useOwnerWindow(ref) hook). And any
document.createElement for an offscreen canvas
has to go through
someExistingNode.ownerDocument.createElement so
the node belongs to the popout's DOM rather than
the parent's.

## Result

Finterm is live at
finterm.xyz — open it, type
a ticker, and a chart, SEC fundamentals, options
chain with Greeks, and analyst estimates open as
draggable windows. Everything described above runs
in Cloudflare's edge: no Node server, no cold
starts to speak of.

Happy to go deeper on any of the above if there's
interest.