US & TW Stock PK: multi-stock return comparison

A minimal “Taiwan multi-stock PK” tool: pick 2–5 stocks, a date range and an amount, and instantly see each stock’s total return (dividends included), final value, and the gap versus a baseline (0050 by default). The winner is highlighted, plotted as a dual-axis growth chart (money on the left, return % on the right, hover for any day’s value and %).

Independently deployed on the full Cloudflare stack:

• Pages (Astro): all computation and a hand-rolled SVG growth chart on the client (no charting dependency)
• Worker: proxies the Yahoo Finance chart API (avoids CORS + edge caching), returning dividend/split-adjusted series
• D1: visitor counter (hashed IP, raw IP never stored)
• Stock list generated at build time from public data (code + Chinese-name autocomplete, TWSE & TPEx)

Engineering details: corrects splits Yahoo left unadjusted (Taiwan’s ±10% daily limit makes an anomalous same-day ratio unambiguously a split → the artificial discontinuity is smoothed away, e.g. 0052’s ~7:1 split in 2025-11), fair comparison over the common trading window across all picks, URL-based sharing (comparison state encoded in the URL, and shortened on demand via my other project (devbox’s URL shortener), wired together with a Cloudflare Service Binding, so the short links even show up in devbox’s click analytics), and security (the proxy guards against SSRF and abuse; the token lives only in a Worker secret).