feat(graphiql): add data fetching hooks

[amcaplan]

WHY are these changes introduced?

This PR adds custom React hooks for server health monitoring and data fetching. This is the sixth PR in the 8-PR migration stack.

Context: The current template-based GraphiQL implementation uses vanilla JavaScript with setInterval to poll the server for health status and app installation state. By creating reusable React hooks, we can:

• Integrate polling with React's component lifecycle
• Automatically clean up intervals when components unmount
• Use React state management for server status
• Make polling logic testable and reusable
• Handle errors gracefully without breaking the UI

WHAT is this pull request doing?

This PR adds two custom hooks that replace vanilla JavaScript polling with React-based data fetching.

Key Changes:

1. usePolling Hook (src/hooks/usePolling.ts): A generic hook for interval-based polling with proper cleanup and error handling.

Features:

• Calls a callback function at regular intervals
• Supports async functions (returns Promise)
• Handles both sync and async errors gracefully (logs but doesn't crash)
• Uses useRef to avoid stale closure issues
• Calls callback immediately on mount, then at intervals
• Automatically cleans up interval on unmount
• Can be enabled/disabled dynamically

Usage:

usePolling(async () => {
  await checkServerHealth()
}, {
  interval: 2000,       // Poll every 2 seconds
  enabled: isActive     // Optional: control polling
})

2. useServerStatus Hook (src/hooks/useServerStatus.ts): Monitors server health and app installation status by polling two endpoints.

Two Polling Mechanisms:

Ping Polling (/graphiql/ping - every 2 seconds by default):

• Checks if dev server is running
• Uses timeout mechanism: marks server dead if no response within 3 seconds
• Clears pending timeouts on successful response
• Updates serverIsLive state

Status Polling (/graphiql/status - every 5 seconds by default):

• Checks if app is installed in store
• Fetches store information (storeFqdn, appName, appUrl)
• Updates appIsInstalled state and store info

Return Value:

interface ServerStatus {
  serverIsLive: boolean      // Server is responding to pings
  appIsInstalled: boolean    // App is installed in store
  storeFqdn?: string        // e.g., "my-store.myshopify.com"
  appName?: string          // e.g., "My Test App"
  appUrl?: string           // e.g., "http://localhost:3000"
}

Usage:

const status = useServerStatus({
  baseUrl: 'http://localhost:3457',
  pingInterval: 2000,     // Optional: default 2000ms
  statusInterval: 5000,   // Optional: default 5000ms
  pingTimeout: 3000,      // Optional: default 3000ms
})

// Use status in components
<StatusBadge status={status} />
<ErrorBanner isVisible={!status.serverIsLive} />
<LinkPills status={status} />

Error Handling:

• Network errors are caught and treated as "server down" or "app not installed"
• Polling continues even if individual requests fail
• No errors are thrown to crash the application
• Uses intentional catch-all blocks (with eslint disable comments)

Replaces:

• Vanilla JavaScript setInterval polling logic
• Manual timeout tracking and cleanup
• Direct DOM manipulation based on server status

Testing:

• 386 lines of comprehensive tests (176 for usePolling, 210 for useServerStatus)
• Tests interval execution
• Tests error handling
• Tests cleanup on unmount
• Tests timeout behavior
• Tests state updates

Files Added:

• src/hooks/usePolling.ts - Generic polling hook (46 lines)
• src/hooks/usePolling.test.ts - Tests (176 lines)
• src/hooks/useServerStatus.ts - Server status hook (102 lines)
• src/hooks/useServerStatus.test.ts - Tests (210 lines)
• src/hooks/index.ts - Barrel exports

Dependencies

Builds on:

• PR #6578 (package foundation)
• PR #6579 (validation and types)

Used by:

• PR #6580 (StatusBadge, ErrorBanner, LinkPills need ServerStatus type)
• Subsequent PRs will use these hooks in the main layout

How to test your changes?

# Run hook tests
pnpm --filter @shopify/graphiql-console test usePolling.test.ts
pnpm --filter @shopify/graphiql-console test useServerStatus.test.ts

# Type check
pnpm --filter @shopify/graphiql-console tsc --noEmit

# All 386 lines of tests should pass, covering:
# - Polling interval execution
# - Immediate first call on mount
# - Interval cleanup on unmount
# - Error handling (sync and async)
# - Enabled/disabled toggling
# - Server ping timeout behavior
# - Status endpoint response parsing
# - Network error handling

Manual Testing: You can test the hooks in the App component:

import {useServerStatus} from './hooks'

const status = useServerStatus({
  baseUrl: 'http://localhost:3457'
})

console.log('Server status:', status)

// Stop the dev server and watch serverIsLive change to false
// Restart it and watch it change back to true

Measuring impact

• [x] n/a - these are foundational data fetching hooks

Checklist

• [x] I've considered possible cross-platform impacts (Mac, Linux, Windows)
• [x] I've considered possible documentation changes

[amcaplan]

[!WARNING] This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite. Learn more

• #6585
• #6584
• #6583 👈 (View in Graphite)
• #6582
• #6581
• #6580
• #6579
• #6578
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[github-actions[bot]]

Coverage report

St.:grey_question:	Category	Percentage	Covered / Total
🟡	Statements	79.36% (+0.02% 🔼)	13737/17309
🟡	Branches	73.27% (-0% 🔻)	6721/9173
🟡	Functions	79.38% (-0.03% 🔻)	3545/4466
🟡	Lines	79.73% (+0.03% 🔼)	12969/16267

Show new covered files 🐣

St.:grey_question:	File	Statements	Branches	Functions	Lines
🟢	... / usePolling.ts	100%	100%	83.33%	100%
🟢	... / useServerStatus.ts	82.35%	57.14%	66.67%	88.46%

Test suite run success

3437 tests passing in 1399 suites.

Report generated by 🧪jest coverage report action from eeb9b92fddd558af3c4b125ab14156c27b7af58b