React18 Legacy Context

React 18 Legacy Context Migration

Legacy context (contextTypes, childContextTypes, getChildContext) was deprecated in React 16.3 and warns in React 18.3.1. It is removed in React 19.

This Is Always a Cross-File Migration

Unlike most other migrations that touch one file at a time, context migration requires coordinating:

1. Create the context object (usually a new file)
2. Update the provider component
3. Update every consumer component

Missing any consumer leaves the app broken - it will read from the wrong context or get undefined.

Migration Steps (Always Follow This Order)

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 remain

Scan Commands

# Find all providers
grep -rn "childContextTypes\|getChildContext" src/ --include="*.js" --include="*.jsx" | grep -v "\.test\."