react-native-polyfills

React Native Polyfills for MetaMask Connect

Per-Package Polyfill Requirements

Different integrations need different polyfills. Do not blindly copy the full set:

Polyfill	connect-evm / connect-solana (standalone)	+ wagmi
react-native-get-random-values	RN < 0.72 only (see below)	RN < 0.72 only
Buffer	Safety net only (self-polyfilled by connect-multichain)	Safety net only
window object	Required for correct deeplink/platform detection	Required
Event	Not required	Required (wagmi uses DOM events)
CustomEvent	Not required	Required (wagmi uses DOM events)

Import Order (Critical)

// Entry file (_layout.tsx / index.js) — order is critical
import 'react-native-get-random-values'; // MUST be first (if used)
import './polyfills';                     // window shim, and Event/CustomEvent if using wagmi

Incorrect order causes crypto.getRandomValues is not a function at runtime.

react-native-get-random-values

• Required only for React Native < 0.72 — Hermes 0.72+ exposes globalThis.crypto.getRandomValues natively
• Still recommended as an explicit safety net — especially if any dependency has its own minimum RN version assumptions
• Must be the very first import in the entry file, before anything that touches crypto

Buffer Polyfill

• @metamask/connect-multichain self-polyfills Buffer via its React Native entry point — not needed for the SDK itself
• Still recommended to set global.Buffer = Buffer in polyfills.ts as a safety net for peer deps (e.g. eciesjs, @solana/web3.js) that may load before connect-multichain
• Install: npm install buffer

window Object Polyfill

• Required for correct platform and deeplink behaviour — getPlatformType() in connect-multichain inspects window and global.navigator.product to decide between the deeplink path and the install-modal path
• All window.* accesses inside the SDK are guarded, so code will not crash without it, but isSecure() returns the wrong value and deeplinks will not trigger
• Provide at minimum: location, addEventListener, removeEventListener, dispatchEvent