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

Reference Files

• references/single-context.md - complete migration for one context (theme, auth, etc.) with provider + class consumer + function consumer
• references/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