How do you build and integrate custom Cordova plugins?

Long Answer

When Cordova lacks out-of-the-box support, I treat native plugin integration like a mini product: clear API design, minimal cross-platform surface, strict separation of concerns, and repeatable builds. The goal is to expose a predictable JavaScript interface while respecting the plugin lifecycle and platform quirks on both Android and iOS.

1) Requirements → API contract
Start by drafting the JS API first: methods, events, and error shapes. Keep it capability-driven, not device-driven. For example, instead of startSensorX(), expose startUpdates({frequency, accuracy}). Document return types, Promise/Callback behavior, and error codes in a typed .d.ts. Your façade becomes the stable contract that shields apps from native churn.

2) Project skeleton & plugin.xml
Create a dedicated repo with /src/js, /src/android, /src/ios, and a rigorous plugin.xml. Declare platforms, engine constraints, permissions, config-files, and assets. Wire variables for SDK versions, feature toggles, and entitlements so the plugin can adapt without forking. In plugin.xml, map JS to native classes and define hooks that patch AndroidManifest.xml, build.gradle, Info.plist, and the Podspec cleanly.

3) JavaScript façade & bridge
Implement a tiny façade module that validates input, normalizes options, and calls cordova.exec(success, fail, 'PluginName', 'action', [args]). Avoid leaking native details across the bridge. Prefer Promises and event emitters (or Observables) for streaming updates. Provide polyfills or no-op fallbacks so web previews don’t crash in the WKWebView.

4) Android implementation
On Android, implement a CordovaPlugin with execute(action, args, callbackContext). Route to background threads for I/O using cordova.getThreadPool(). Use modern APIs (Activity Result API) instead of legacy onActivityResult. Handle runtime permissions via requestPermissions and surface granular errors. Keep Gradle tidy: isolate transitive deps, pin versions, and expose them as plugin variables. For the Android/iOS bridge, serialize only plain data (no Binder/Parcelable) across exec.

5) iOS implementation
On iOS, subclass CDVPlugin. Do heavy work off the main thread; hop back to main only for UI. Manage permissions (e.g., camera, location) with clear Info.plist usage strings. If integrating SDKs, wrap delegates into a single internal coordinator so your JS sees a clean stream of events. Use a minimal Podspec with version ranges you test; prefer static frameworks to avoid symbol collisions.

6) Lifecycle and resilience
Respect app lifecycle: pause/resume, background tasks, and process death. Cache init state defensively; rehydrate handles after resume. Feature-detect OS versions and vendor quirks (OEM camera intents, power-save modes). Time-box operations and return deterministic error codes so callers can retry or degrade gracefully. For native plugin integration, build a “circuit breaker” (e.g., disable streaming if the OS feature is missing).

7) Testing & CI
Ship example apps under examples/ to exercise the API. In CI, run cordova build android and cordova build ios on a matrix of SDK versions. Add JS unit tests for parameter validation and a small Playwright/Appium flow for smoke checks. Lint Objective-C/Swift/Kotlin; run static analysis. Cache Gradle/CocoaPods to speed builds. This catches Cordova engine and toolchain drift early.

8) Performance & memory
Keep native layers thin. Batch messages to the JS thread; for high-frequency streams, coalesce updates (e.g., every 100ms). Avoid retaining Activities/ViewControllers. Release listeners on onPause/onReset. Use structured cloning-friendly payloads (plain objects, arrays) to minimize bridge overhead.

9) Versioning & compatibility
Adopt semantic versioning. In minors, add capability flags; in majors, allow breaking changes with a migration guide. Maintain a compatibility table: Cordova CLI, platform versions, Android/iOS SDK ranges, and browser engine versions. Provide deprecation warnings in JS (once per session), pointing to new options.

10) Documentation & supportability
Docs should include install steps, variables, platform notes, permission prompts, known limitations, and code samples. Add troubleshooting for common build issues (Xcode signing, Gradle plugin clashes). Offer a minimal Android/iOS bridge diagram to help teams debug crossings. Good docs are the cheapest “anti-flake” you’ll ever ship.

Together, this playbook yields custom Cordova plugins that feel first-class: a stable JS API, carefully scoped native code, predictable builds, and resilience across OS updates. You win both speed (because the bridge is simple) and maintainability (because the native complexity is cordoned off).

‍

Table

‍

Common Mistakes

Leaking native details into JS (callbacks tied to specific Activities/VCs). Skipping plugin.xml hygiene and hard-patching manifests or plists. Doing heavy work on the main thread and blocking UI. Ignoring runtime permissions, then crashing on first use. Sending complex objects across the bridge (Parcelables, custom classes) that fail to serialize. Mixing business logic into the JS façade instead of a thin adapter. No CI for Android/iOS, so toolchain drift explodes on release day. Relying on fixed SDK versions without a compatibility table. Missing lifecycle cleanup—listeners survive pause/resume and cause ghost callbacks.

‍

Sample Answers (Junior / Mid / Senior)

Junior:
“I’d design a small JS façade that calls cordova.exec, then implement native code for Android/iOS. I’d use plugin.xml to declare permissions and add TypeScript types. I handle permissions and return Promises with clear errors.”

Mid:
“My native plugin integration keeps heavy work off the main thread. I feature-detect APIs, manage runtime permissions, and normalize results before crossing the bridge. CI builds Android and iOS examples; docs include install steps and permission prompts.”

Senior:
“I start with a typed JavaScript interface and deprecation strategy. The native layers are thin, background-safe, and lifecycle-aware. We batch events, coalesce updates, and expose capability flags. plugin.xml drives manifests/podspecs. CI runs matrix builds, e2e samples, and static analysis. We maintain a compatibility table and ship migration notes with SemVer.”

‍

Evaluation Criteria

Strong answers show a JS-first contract, disciplined plugin.xml, and thin, async native layers with proper permission and lifecycle handling. They mention Android/iOS bridge details (threading, serialization), plugin lifecycle (pause/resume/reset), and CI against multiple SDKs. Look for typed APIs, Promises/events, and defensive feature detection. Bonus: capability flags, deprecations, and a compatibility table. Weak answers jump straight to native code, block the main thread, skip permissions/lifecycle, or lack tests and documentation—guaranteed flake and painful upgrades.

‍

Preparation Tips

Build a tiny example plugin (e.g., device info + sensor stream). Draft a typed JS façade with Promises and an event emitter. Map to native: CordovaPlugin on Android with background work; CDVPlugin on iOS with Info.plist entries. Wire plugin.xml to inject permissions and Podspec/Gradle bits. Add an examples/ app and CI that performs cordova platform add, builds both targets, and runs smoke tests. Practice debugging: permission denial, app resume, and serialization errors. Write a compatibility table and migration note to simulate a major update. This rehearsal bakes maintainability into your Cordova custom plugins.

‍

Real-world Context

A media app needed low-latency audio mixing absent in core Cordova. The team shipped a plugin with a strict JS façade and native mixers on threads. They cached state on pause/resume and coalesced events to cut bridge chatter. CI built Android/iOS examples nightly; a compatibility table mapped Cordova and SDK ranges. Upgrades later (new iOS audio session rules) required only native tweaks—the JS API stayed stable. Another team rushed a camera plugin, blocked the main thread, and hard-patched manifests; it broke on Android 13. After refactor (proper plugin.xml, runtime permissions, async I/O), flakiness vanished and releases calmed down.

‍

Key Takeaways

• Design a typed JavaScript interface first; keep native layers thin.
  
• Let plugin.xml drive manifests, permissions, and build metadata.
  
• Handle permissions, threading, and the plugin lifecycle correctly.
  
• Keep bridge payloads simple; batch events and coalesce updates.
  
• Ship CI matrix builds, docs, and a compatibility table with SemVer.
  
  

Practice Exercise

Scenario:
You must expose a secure biometric unlock not available via stock Cordova. The plugin must support iOS/Android, handle permission prompts, and survive pause/resume.

Tasks:

1. API contract: Design a typed JS façade: isAvailable(), authenticate({reason}) → Promise<{token}>, onStatus(cb). Define error codes (denied, lockout, unavailable).
   
2. Bridge: Implement cordova.exec calls; normalize results to plain objects. Add an event emitter for status updates.
   
3. Android: Use BiometricPrompt with an executor on a background thread; handle lifecycle via Fragment. Request runtime permissions if needed; return deterministic errors.
   
4. iOS: Wrap LAContext in a CDVPlugin; do work off main thread, hop to main for UI. Provide Info.plist usage strings.
   
5. plugin.xml: Declare permissions, config-files, Podspec/Gradle deps as variables.
   
6. Lifecycle: Cache state, release listeners on onPause/onReset, rehydrate on resume.
   
7. CI & Samples: Add examples/ app; CI builds both platforms, runs smoke flows; lint Swift/Kotlin.
   
8. Docs & Versioning: Write install steps, capability matrix, and a SemVer changelog.
   
   

Deliverable:
Repo + samples + CI logs showing successful Android/iOS builds, a stable JavaScript interface, and documentation proving maintainable native plugin integration that’s ready for future updates.