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Use getRandomValues in React Native

If you have been coding React Native for a while you may have noticed that some of Web APIs aren’t implemented in React Native.

One useful Web API that can be nice to have is Crypto.getRandomValues(). It allows us to generate cryptographically secure random values.

Why do we need it?

const array = new Uint32Array(3);
console.log(array); // Uint32Array(3) [910455739, 2479945565, 2186657619, buffer: ArrayBuffer(12), byteLength: 12, byteOffset: 0, length: 3, Symbol(Symbol.toStringTag): 'Uint32Array']

On web the code would simply fill array with cryptographically secure random values and logs the array together with the values generated, but on React Native this will throw an error Can't find variable: crypto.

Also, some libraries like uuid depends on this API. If you ever to use some libraries that depend on this API you will need the polyfill.

import { v4 as uuidv4 } from 'uuid';
const uuid = uuidv4();

The above code will throw crypto.getRandomValues() is not supported in React Native.

The Polyfill

That’s where react-native-get-random-values saves us. It defines the function crypto.getRandomValues so that we can work on our React Native project just like on how we work on web.

We can just install the polyfill.

$ yarn add react-native-get-random-values

Run the next command if you’re also supporting iOS.

$ npx pod-install ios

Since this module contains native code, you need to rebuild your project.

Then in your index.js:

import 'react-native-get-random-values';
import { AppRegistry } from 'react-native';
// ... your other codes

After this, errors such as Can't find variable: crypto and crypto.getRandomValues() is not supported should now disappear.

That’s it, we now have successfully installed a polyfill to be able to work with JavaScript libraries that depends on Web API to work with React Native.

This post is licensed under CC BY 4.0 by the author.

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