Lesson 05 | Act 5: History and Responsiveness

⏱ Est. reading time: 3 min Updated on 5/7/2026

Act 5: History and Responsiveness (Episodes 11-12)

Final feature polishing — making it feel like a real product

Episode 11: Remember What Was Calculated

Scene: Calculated and gone? Users want to look back.

  • History data structure: FIFO queue, max 10 entries, addEntry automatically evicts the oldest
  • localStorage persistence: JSON serialization, survives page refreshes, silently ignores corrupt data
  • History panel: 300ms slide-out animation (width: 0 → width: 240px + transition)
  • Mobile: position: fixed full-screen overlay to avoid squishing the calculator
  • XSS security: Use textContent instead of innerHTML — why it matters (user input might contain HTML)
  • Hide history panel in elderly mode (ELDR-05: simplify UI, elderly users don't need history)
  • Core concept: localStorage allows the browser to "remember" things

Output Files:

  • index.html — <aside class="history-panel"> + history toggle button
  • style.css — History panel styles + slide-out animation + mobile overlay
  • app.js — History management (saveHistory / loadHistory / renderHistory / clearHistoryUI)
  • tests/history/history-fifo.test.js — FIFO queue tests

Command: /gsd-plan-phase 4, /gsd-execute-phase 4

Episode 12: Works on Mobile Too

Scene: Perfect on desktop, but open it on a phone — layout collapses.

  • Responsive breakpoints: desktop (>1024px) / tablet (640-1024px) / mobile (<640px)
  • CSS Media Query: 3 layouts, handled by one style.css
  • Mobile adaptation: grid-template-columns: repeat(4, 1fr) + width: 100% + border-radius: 0
  • Elderly mode on mobile: Buttons 64px (slightly smaller than 68px desktop but still compliant), fonts 22px/32px
  • Elderly mode mobile background pure white #ffffff, seamless visuals
  • History panel mobile position: fixed full-screen cover, z-index: 10
  • Testing across different widths: Simulate using browser DevTools
  • Core concept: Responsiveness isn't scaling, it's rearranging layouts

Output Files:

  • style.css — 3 breakpoint media queries + elderly mode mobile adaptations

Command: /gsd-execute-phase 4 (continued)

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