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Get Started Free →Provides the complete migration pattern for React legacy context API (contextTypes, childContextTypes, getChildContext) to the modern createContext API. Use this skill whenever migrating legacy context in class components - this is always a cross-file migration requiring the provider AND all consumers to be updated together. Use it before touching any contextTypes or childContextTypes code, because migrating only the provider without the consumers (or vice versa) will cause a runtime failure. Al
.claude/skills/react18-legacy-context/SKILL.md| Test case | Without → With | Effect | Δ tokens | Δ turns |
|---|---|---|---|---|
| case-08 | ✗→✓ | ▲ Improved | — | — |
| case-14 | ✗→✓ | ▲ Improved | — | — |
| case-09 | ✗→✓ | ▲ Improved | — | — |
| case-13 | ✗→✓ | ▲ Improved | — | — |
| case-03 | ✗→✓ | ▲ Improved | — | — |
Legacy context (contextTypes, childContextTypes, getChildContext) was deprecated in React 16.3 and warns in React 18.3.1. It is removed in React 19.
Unlike most other migrations that touch one file at a time, context migration requires coordinating:
Missing any consumer leaves the app broken - it will read from the wrong context or get undefined.
Step 1: Find the provider (childContextTypes + getChildContext)
Step 2: Find ALL consumers (contextTypes)
Step 3: Create the context file
Step 4: Update the provider
Step 5: Update each consumer (class components → contextType, function components → useContext)
Step 6: Verify - run the app, check no legacy context warnings remainbash# Find all providers grep -rn "childContextTypes\|getChildContext" src/ --include="*.js" --include="*.jsx" | grep -v "\.test\." # Find all consumers grep -rn "contextTypes\s*=" src/ --include="*.js" --include="*.jsx" | grep -v "\.test\." # Find this.context usage (may be legacy or modern - check which) grep -rn "this\.context\." src/ --include="*.js" --include="*.jsx" | grep -v "\.test\."
references/single-context.md - complete migration for one context (theme, auth, etc.) with provider + class consumer + function consumerreferences/multi-context.md - apps with multiple legacy contexts (nested providers, multiple consumers of different contexts)references/context-file-template.md - the standard file structure for a new context module| Case | Status | Duration (ms) | Turns | Tokens | Tool calls | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Without | With | Δ | Without | With | Δ | Without | With | Δ | Without | With | Δ | ||
case-08 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
case-14 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
case-05 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-02 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-09 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
case-19 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-17 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-06 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-18 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-13 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
case-04 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-03 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
case-10 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-21 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-11 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-15 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
case-01 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-07 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
case-20 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-22 | fail→fail | — | — | — | — | — | — | — | — | — | — | — | — |
case-12 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
case-16 | fail→pass | — | — | — | — | — | — | — | — | — | — | — | — |
DecimalAI ran this skill against gemini-3.6-flash twice over the same eval suite — once with the skill loaded and once without — and compared the two runs case by case. 22 cases were attempted. The headline lift of +41 percentage points is the difference between those two pass rates over the 22 comparable cases.
The per-case answers from this run were removed by the retention sweep, so the case table below shows the verdicts without the text either arm produced. The counts above were recorded at the time and are unaffected. Answers are now kept for 180 days.
Other measured skills in the registry, with their headline benchmark lift.