Mentoring Junior Mobile Devs

Q: Web React hire - what transfers?

Component thinking, hooks, and testing mindset transfer. New: Metro, simulators, native boundaries, store release clocks, platform a11y services.

Q: How hands-on should mentors be?

Pair on days 1–5 for environment and first merge; review with teaching comments week 2–4; delegate bounded features by week 3–6 if capstone merged.

Q: What if buddy is too busy?

Lead assigns alternate buddy for reviews within 24h; do not leave first PR idle - kills confidence.

Simulator skills, debugging, and safe first PRs for engineers new to Expo SDK 57. Mobile mentoring fails when juniors fight Metro day three while seniors expect feature velocity - structure the first two weeks deliberately.

Recipe

Quick-reference mentor card - assign buddy + milestones.

Week 1 milestones:
  Day 1  Metro green + expo-doctor (iPhone 16 + Pixel 8 emu)
  Day 2  Tiny UI PR merged (subtitle, test, screenshots)
  Day 3  Trace one feature: app/ route → features/ screen → hook
  Day 4  Fix one lint/a11y review comment with TalkBack check
  Day 5  Install preview EAS build on personal device
 
Safe first PR types:
  ✅ Copy, spacing, RNTL test, accessibilityLabel
  ✅ New screen behind existing tab pattern (buddy reviews route)
  ⚠️  New npm dependency (buddy + lead review)
  🚫 Solo app.config.ts / eas.json / config plugin / native module

# Mentor runs this with mentee on day 1
npx expo-doctor
npx expo start
# Press i → iOS   Press a → Android
# Shift+I / Shift+A → pick standard team devices

When to reach for this:

Hiring web React devs onto mobile squads.
Intern or bootcamp graduate joining mid-sprint.
Senior IC asked to "buddy" without a written path - use First-Week Learning Path as spine.

Working Example

Simulator skills curriculum

Day	Skill	Exercise
1	Boot simulators	`npx expo start` → `i` / `a`; screenshot both platforms
2	Device picker	`Shift+I` choose iPhone SE - layout still readable
3	Reload vs dev menu	`r` reload; dev menu → Fast Refresh verify
4	Accessibility	VoiceOver ⌘F5; navigate one form with labels
5	Physical device	Install preview build; compare safe area to sim

Deep reference: iOS Simulator & Android Emulator.

# Standard team device names (document in CONTRIBUTING.md)
xcrun simctl list devices available | grep "iPhone 16"
# Android: Pixel 8 API 35 in AVD Manager

Safe first PR - "Explore subtitle"

Scope: One TSX file in features/, thin route re-export, one RNTL test, PR screenshots.

// features/explore/screens/ExploreScreen.tsx - mentee edits here only
import { Text, View } from "react-native";
 
export function ExploreScreen() {
  return (
    <View style={{ flex: 1, padding: 16 }}>
      <Text accessibilityRole="header">Explore</Text>
      <Text>Discover tips curated for you.</Text>
    </View>
  );
}

// __tests__/ExploreScreen.test.tsx
import { render, screen } from "@testing-library/react-native";
import { ExploreScreen } from "@/features/explore/screens/ExploreScreen";
 
test("shows curated subtitle", () => {
  render(<ExploreScreen />);
  expect(screen.getByText(/curated for you/i)).toBeTruthy();
});

Mentor review teaches:

PR template checklist from Code Review Standards for RN
Why route file stays one line - Mobile Architecture Basics
Attach iOS + Android screenshots before requesting review

Debugging ladder (teach in order)

1. Read the redbox / LogBox - full message, file, line
2. React DevTools - props/state wrong vs layout wrong
3. Metro terminal - transform / resolution errors
4. npx expo-doctor - version skew
5. eas build preview - reproduces native-only failures
6. Xcode / Android Studio logs - last resort; pair only

// Common junior mistake - mentor demo fix
// ❌ Inline renderItem invalidates list memo
<FlashList renderItem={({ item }) => <Row item={item} />} ... />
 
// ✅ Module-level or useCallback
const renderItem = useCallback(({ item }: { item: Item }) => <Row item={item} />, []);

Pair on first Hermes undefined is not a function - teach npm why <pkg> and lockfile hygiene, not random cache clears.

PRs to defer until mid-level

Topic	Why wait	Mentor alternative
`app.config.ts` plugins	Store rejection risk	Pair read-only walkthrough
`eas.json` credentials	Org-wide blast radius	Shadow `eas build:list`
Native module install	Dev client + OTA rules	Watch lead merge similar PR
Navigation restructure	Dual back stacks	Bugfix in existing stack first
TanStack Query cache design	Global data bugs	Add field to existing query

Align promotion evidence with Junior → Mid RN Leveling.

Weekly mentor sync (15 minutes)

## Mentee: @name - week 2
 
Shipped:
- PR #412 Explore subtitle (merged)
- Preview build on Android device
 
Stuck:
- useLocalSearchParams typing - read typed routes doc
 
Next:
- Add Tips row + Link to /tips (capstone)
 
Mentor action:
- Pair 30m on Query hook Thursday

Feed "stuck" items into onboarding doc PRs - Onboarding Basics.

Gotchas

"Works on my machine" - Junior uses Expo Go; app needs dev client. Fix: Day-one README clarity; preview build by day five.
Throwing juniors on hotfix Friday - No rollback literacy. Fix: Hotfixes shadowed; first solo fix is Monday OTA with template.
Review nitpicks without teaching - Style comments without "why" do not build mobile judgment. Fix: One teaching comment per review (a11y, perf, or boundary).
Skipping Android - iOS-only habit on Android-majority user base. Fix: Both screenshots required from week one.

Alternatives

Approach	Use When	Don't Use When
Buddy + written path	Default	"Sink or swim" on legacy brownfield
Mob programming week one	Complex domain (fintech)	Simple CRUD - overkill
Formal training budget	Large hiring wave	One hire - use internal docs
Rotating mentors	Broad exposure	Needs continuity for first PRs

FAQs

Web React hire - what transfers?

Component thinking, hooks, and testing mindset transfer. New: Metro, simulators, native boundaries, store release clocks, platform a11y services.

How hands-on should mentors be?

Pair on days 1–5 for environment and first merge; review with teaching comments week 2–4; delegate bounded features by week 3–6 if capstone merged.

Junior wants to learn native modules immediately?

Redirect to Expo SDK modules first. Custom native is mid+ competency unless hired as platform engineer - see Native vs JavaScript Trade-offs.

What if buddy is too busy?

Lead assigns alternate buddy for reviews within 24h; do not leave first PR idle - kills confidence.

First-Week Learning Path - five-day capstone cookbook
Onboarding Basics - machine setup
Junior → Mid RN Leveling - skills matrix
Codebase Tour Checklist - tiered repo tour
Pairing & Mob on Mobile - session norms
Code Review Standards for RN - teach review checklist
iOS Simulator & Android Emulator - device matrix

Stack versions: This page was written for React 19.2.3, React Native 0.86.0, and Expo SDK 57 (expo ~57.0.4).

Recipe

Quick-reference mentor card - assign buddy + milestones.

Week 1 milestones:
  Day 1  Metro green + expo-doctor (iPhone 16 + Pixel 8 emu)
  Day 2  Tiny UI PR merged (subtitle, test, screenshots)
  Day 3  Trace one feature: app/ route → features/ screen → hook
  Day 4  Fix one lint/a11y review comment with TalkBack check
  Day 5  Install preview EAS build on personal device
 
Safe first PR types:
  ✅ Copy, spacing, RNTL test, accessibilityLabel
  ✅ New screen behind existing tab pattern (buddy reviews route)
  ⚠️  New npm dependency (buddy + lead review)
  🚫 Solo app.config.ts / eas.json / config plugin / native module

# Mentor runs this with mentee on day 1
npx expo-doctor
npx expo start
# Press i → iOS   Press a → Android
# Shift+I / Shift+A → pick standard team devices

When to reach for this:

Hiring web React devs onto mobile squads.
Intern or bootcamp graduate joining mid-sprint.
Senior IC asked to "buddy" without a written path - use First-Week Learning Path as spine.

Working Example

Simulator skills curriculum

Day	Skill	Exercise
1	Boot simulators	`npx expo start` → `i` / `a`; screenshot both platforms
2	Device picker	`Shift+I` choose iPhone SE - layout still readable
3	Reload vs dev menu	`r` reload; dev menu → Fast Refresh verify
4	Accessibility	VoiceOver ⌘F5; navigate one form with labels
5	Physical device	Install preview build; compare safe area to sim

Deep reference: iOS Simulator & Android Emulator.

# Standard team device names (document in CONTRIBUTING.md)
xcrun simctl list devices available | grep "iPhone 16"
# Android: Pixel 8 API 35 in AVD Manager

Safe first PR - "Explore subtitle"

Scope: One TSX file in features/, thin route re-export, one RNTL test, PR screenshots.

// features/explore/screens/ExploreScreen.tsx - mentee edits here only
import { Text, View } from "react-native";
 
export function ExploreScreen() {
  return (
    <View style={{ flex: 1, padding: 16 }}>
      <Text accessibilityRole="header">Explore</Text>
      <Text>Discover tips curated for you.</Text>
    </View>
  );
}

// __tests__/ExploreScreen.test.tsx
import { render, screen } from "@testing-library/react-native";
import { ExploreScreen } from "@/features/explore/screens/ExploreScreen";
 
test("shows curated subtitle", () => {
  render(<ExploreScreen />);
  expect(screen.getByText(/curated for you/i)).toBeTruthy();
});

Mentor review teaches:

PR template checklist from Code Review Standards for RN
Why route file stays one line - Mobile Architecture Basics
Attach iOS + Android screenshots before requesting review

Debugging ladder (teach in order)

1. Read the redbox / LogBox - full message, file, line
2. React DevTools - props/state wrong vs layout wrong
3. Metro terminal - transform / resolution errors
4. npx expo-doctor - version skew
5. eas build preview - reproduces native-only failures
6. Xcode / Android Studio logs - last resort; pair only

// Common junior mistake - mentor demo fix
// ❌ Inline renderItem invalidates list memo
<FlashList renderItem={({ item }) => <Row item={item} />} ... />
 
// ✅ Module-level or useCallback
const renderItem = useCallback(({ item }: { item: Item }) => <Row item={item} />, []);

Pair on first Hermes undefined is not a function - teach npm why <pkg> and lockfile hygiene, not random cache clears.

PRs to defer until mid-level

Topic	Why wait	Mentor alternative
`app.config.ts` plugins	Store rejection risk	Pair read-only walkthrough
`eas.json` credentials	Org-wide blast radius	Shadow `eas build:list`
Native module install	Dev client + OTA rules	Watch lead merge similar PR
Navigation restructure	Dual back stacks	Bugfix in existing stack first
TanStack Query cache design	Global data bugs	Add field to existing query

Align promotion evidence with Junior → Mid RN Leveling.

Weekly mentor sync (15 minutes)

## Mentee: @name - week 2
 
Shipped:
- PR #412 Explore subtitle (merged)
- Preview build on Android device
 
Stuck:
- useLocalSearchParams typing - read typed routes doc
 
Next:
- Add Tips row + Link to /tips (capstone)
 
Mentor action:
- Pair 30m on Query hook Thursday

Feed "stuck" items into onboarding doc PRs - Onboarding Basics.

Gotchas

"Works on my machine" - Junior uses Expo Go; app needs dev client. Fix: Day-one README clarity; preview build by day five.
Throwing juniors on hotfix Friday - No rollback literacy. Fix: Hotfixes shadowed; first solo fix is Monday OTA with template.
Review nitpicks without teaching - Style comments without "why" do not build mobile judgment. Fix: One teaching comment per review (a11y, perf, or boundary).
Skipping Android - iOS-only habit on Android-majority user base. Fix: Both screenshots required from week one.

Alternatives

Approach	Use When	Don't Use When
Buddy + written path	Default	"Sink or swim" on legacy brownfield
Mob programming week one	Complex domain (fintech)	Simple CRUD - overkill
Formal training budget	Large hiring wave	One hire - use internal docs
Rotating mentors	Broad exposure	Needs continuity for first PRs

FAQs

Web React hire - what transfers?

Component thinking, hooks, and testing mindset transfer. New: Metro, simulators, native boundaries, store release clocks, platform a11y services.

How hands-on should mentors be?

Pair on days 1–5 for environment and first merge; review with teaching comments week 2–4; delegate bounded features by week 3–6 if capstone merged.

Junior wants to learn native modules immediately?

Redirect to Expo SDK modules first. Custom native is mid+ competency unless hired as platform engineer - see Native vs JavaScript Trade-offs.

What if buddy is too busy?

Lead assigns alternate buddy for reviews within 24h; do not leave first PR idle - kills confidence.

First-Week Learning Path - five-day capstone cookbook
Onboarding Basics - machine setup
Junior → Mid RN Leveling - skills matrix
Codebase Tour Checklist - tiered repo tour
Pairing & Mob on Mobile - session norms
Code Review Standards for RN - teach review checklist
iOS Simulator & Android Emulator - device matrix

Stack versions: This page was written for React 19.2.3, React Native 0.86.0, and Expo SDK 57 (expo ~57.0.4).

Mentoring Junior Mobile Devs

Search Documentation

Mentoring Junior Mobile Devs