How to optimize React Native App

1. Use FlatList  to render large lists in React Native

          If you have a large list, rendering all the items at once can cause a performance issue, but lazy loading with FlatList will improve performance

import React from 'react'
import {FlatList} from 'react-native'

2. Remove all console statements

While you could install some plugins such as 
babel-plugin-transform-remove-console to remove these statements
from production

3. Memoize expensive computations

    React introduced the memo HOC (Higher Order Component) for preventing unnecessary re-rendering and the useMemo hook for optimizing expensive computations.

4. Adjust (resize and scale down) image sizes

   Images can contribute significantly to performance issues in React Native applications. So use relevant sized Images to increase the loading performance of your App

5. Remove unnecessary libraries and features

Each library in a React or React Native application leaves some footprint on the application. This is why you should only add libraries and features you need in your app and remove irrelevant dependencies and libraries. Animations, navigations, tabs, and other features can contribute to the screen load time and so the more they are on the screen, the worse the performance.

6. Use Hermes

    Hermes is a JavaScript Engine developed by Facebook in 2019. It is one of the must-have features for improving app performance, reducing memory usage, decreasing app size, and improving the app start-up time.

     Hermes is not currently enabled by default in React Native but you can easily enable it in your app.

     To enable Hermes on Android, edit your android/app/build.gradle file and add the following rules.

project.ext.react = [
      entryFile: "index.js",
      enableHermes: true
  ]