For JavaScript developers who want to learn React Native. Learn how to build not just an app, but a Product.

About this Course

Where does React Native fall within app categories? Should you invest in it?

The Value of Building Real-World Apps in React Native

Once you get the hang of the ecosystem around React Native, building apps will be the easy part. We need to consider storyboarding - the art of the right way to build apps.

Storyboarding a React Native App's Components and Flow

Starting from the ground up? We'll look at the structure of the boilerplate code. An opinionated way to build apps, inspired by several apps in production.

Bootstrapping a React Native App With Boilerplate

Set up, build and run the boilerplate code, with a battle-hardened template and all the necessary tools already integrated.

How to Start Building a React Native iOS and Android App

Getting Started

Stacked app or tabbed navigation, drawer menus and modals, and what's the best place to load user sessions, and other application data.

Getting Started With React Native Navigation

Set the app's launch screen and icons. Learn what image to put in native and what to bundle with React Native. Set the tab bar icons.

Set App Logos, Launch Screens, and Icons in React Native

Learn about the screen lifecycle, and customize the app bar and the back button. We will also look at perceived load time and how to manage it.

Optimize Perceived Performance With React Native Lifecycle

Navigation and Screens

Atomic design is a mental model of how the UI should be built and laid out. It is at the core of how we are going to build our apps.

Intro to Atomic Design Patterns [with examples]

To build a design system we need to start by defining a typography; defining the fonts, colors and icons of the app.

Building a Typography Design System in React Native

Global styles help lay the design structure the app should follow. We'll extend our typography from the previous lesson to define styles, mainly for atoms, molecules and organisms.

How to Set Global Styles in React Native

Should we use images or SVGs? Should we be putting them in the React Native bundle, or on native and save OTA bandwidth? Let's look at the best practices.

SVG vs PNG: Which Image Format to Use in a React Native App

We'll look at the Atomic design pattern's atoms and molecules; what they are and how they help build the design system of the app.

Customizing React Native Elements With Global Style

Built using atoms and molecules, Organisms are the complex components that deliver specific features. They are at the core of an app that delivers a consistent UX.

Combining React Elements Into Widgets

What happens when we press a button on an app vs when we press a button on a web page? That difference is User Experience.

How to Build a Design System for Optimal User Experience

Design System

State Management in React Native has similar options to React.

How State Management Works in React Native vs React

Context API provides a way to pass data through the component tree - no more prop-drilling!

Using React Context API to Pass Data to React Components

Intro to Managing React Application State With Flux and Redux

State Management

The very reliable "fetch". Learn the best practices for structuring the app's services and APIs to make them resilient to change.

Making API Calls in a React Native App With fetch and Axios

Middleware allows for side-effects to be executed without blocking state updates. Logger and Analytics make for perfect use cases.

Using Middleware to Run React API Calls in the Background

AsyncStorage is an asynchronous, unencrypted, persistent, key-value storage system for React Native.

How to Store User Login Data With React Native Async Storage

API calls and Middlewares

How to debug a React Native app and a look at a working combination of tools and techniques. Remote Debugger, DevTools and error boundaries.

Intro to Debugging React Native With iOS and Android DevTools

React Native Debugger and Flipper; the evolution of debugging options at React Native.

Using React Native Debugger to Optimize an App

Running on a real device is imperative to testing how the app will actually perform.

How to Test React Native Apps on iOS and Android Devices

Debugging

How JavaScript works. Learn best practices, find the node that is taking time to render, improve FPS performance, learn when to do image caching and find out about Hermes.

How to Improve JavaScript Performance and Boost Frame Rates

Does your app have lot of images or tabs? Thousands of items or an endless scroll? Let's look at how to handle it best in React Native.

Use List Virtualization to Optimize React Native Rendering

Performance

CodePush is Microsoft's App Center cloud service that enables React Native developers to deploy mobile app updates directly to their users' devices.

How to Deploy React Native Apps With Microsoft CodePush

Error reporting in JavaScript and native code

How to Get React Native Error Logs With Sentry

Conclusion

CodePush and Error Reporting

The one-stop solution for micro-animations in a React Native app.

Intro to Building React Native Animations With Lottie

Look no further than React Native SVG for your SVG solution.

Using React Native SVG to Support SVG on iOS and Android

Some common references and special components supported by React Native, Android back handler, and a bit of know-how!

React Native Cheat Sheet

Bonus Content

With React Native, the most important thing is to understand the ecosystem and how it comes together to create an app. By understanding the overall architecture, we will be able to take the full of advantage the platform.

The course will start by covering the fundamentals like setting up the navigation, setting up the screens, styles, and the UI elements, before moving on to more advanced topics such as state management, crash/error reporting, setting up analytics and middlewares, debugging, and performance optimizations. We will also learn how to avoid/fix frame drops - possibly the most watched parameter of any UI application.

We will also build a Design System and will follow the [Atomic Design Pattern](https://atomicdesign.bradfrost.com/chapter-2/) of building layouts. A Design System primarily consists of three parts:
- UI Inventory and Patterns
- Typography
- Spacing and Styles

We will cover these in detail through the modules of the course. We will also learn about the React Native best practices, how to avoid rabbit holes, and focus on building a performant app.

**This is an opinionated way of building apps with React Native**. The fundamentals discussed in the course, like Atomic Design Pattern and Design System, can be applied to building any UI application, not just ones using React Native.

## One Complete App

The course comes with one complete eCommerce sample app that is discussed through the modules of the course.

## Up-to-date

The course builds on an open-source boilerplate template and is kept up to date with React, React Native and dependent library versions. It is also updated with the latest APIs and libraries that are introduced, like Hooks, hermes, flipper etc.

## Why this course

React Native for JavaScript Developers using TypeScript is based on years of experience in building React Native apps on production. The open-source boilerplate code discussed in the course is the platform for multiple apps on App Store and Play Store today. One of them being a Unicorn.

We will take a **Product** based development approach to building apps. React Native abstracts out a lot of platform specific nuances, so wouldn't focusing on building the app as an experience make the most sense. The design pattern will help us exactly with that, and we will put together a structure that is both scalable and extensible. This architecture also helps keep the design separate from the development.

At the end of this course, you will not only be able to build real-world apps with React Native, but also have the fundamentals of building any enterprise UI application.

Discord [channel](https://discord.gg/fz43pNnh)

Code along, and learn to build scalable and performant apps with React Native, from a Product perspective.

The newline Guide to React Native for JavaScript Developers using TypeScript

How to build real world apps. Code along.

How to do state management in React Native

Storyboarding - Build apps from a Product perspective

Understand the React Native ecosystem, the right way

Jumpstart using a template that has ~200 github stars

Architecture that separates design and development

Learn UX best practices and troubleshoot performance bottlenecks

Screens are to apps what pages are to a website, but with one major difference - the screens of an app that are on a stack are all kept in memory, and pressing the Back button will take us to the previous state the screen was in, rather than the view being re-rendered (unless forced), unlike web, where every visit is a re-render.

Every screen in React Native gets all the lifecycle events that are default to React class components. If you have worked with React, these are pretty much the same, apart from two methods that are added by 

The methods are called in the following order when a component is created:

Functional components do not have these lifecycle methods, as the whole function is like one big render function and is executed in one go. However, 

 do provide a way to achieve similar capability. 

 is one such hook, which helps perform side-effects in function components.

useEffect(() => {
  // works like `componentDidMount`

  //good place to make that API call
  async function thatAPIcall() {
    
  }
  thatAPIcall();

  // Gets called after every render
  // on mount, and every re-render
  console.log('render!');

  // similar to `componentWillUnmount`, return a function from here
  return () => console.log('unmounting...');
}, []);   // <--- this is very important

 here. This makes the effect behave similarly to how a 

 does in a class. The array accepts a list of variables to watch for changes, so an empty array means it is not watching anything, thus no re-renders. If we return a function from this, it will be called when the component is unmounted, working like a 

We will talk about state management in functional components in detail in 

While calling any screen, there are three main ways of passing or accessing data. 

Context provides a way to pass data through the component tree without having to pass props down manually at every level.

We will look in detail at these first two ways of handling and passing data in the 

, but for now let's focus the third method, which is more specific to setting up screens:

 attribute that allows us to pass data to the screen being opened.

---
title: Optimize Perceived Performance With React Native Lifecycle
slug: screens
privateVideoUrl: https://fullstack.wistia.com/medias/5cl7s7gasz
isPublicLesson: false
playerCode: #1D5C72
role: LESSON
description: Learn about the screen lifecycle, and customize the app bar and the back button. We will also look at perceived load time and how to manage it.
---

## Screens

Screens are to apps what pages are to a website, but with one major difference - the screens of an app that are on a stack are all kept in memory, and pressing the Back button will take us to the previous state the screen was in, rather than the view being re-rendered (unless forced), unlike web, where every visit is a re-render.

### Lifecycle

Every screen in React Native gets all the lifecycle events that are default to React class components. If you have worked with React, these are pretty much the same, apart from two methods that are added by **React Native Navigation**.

The methods are called in the following order when a component is created:

-   `constructor()` Initializes the component's default `state`.
-   `render()` All rendering-related logic is here. No API calls or data fetching.
-   `componentDidMount()` The best place for API calls, getting data from AsyncStorage and any other data fetching needed to render the view.
-   `componentDidAppear()` Additional method added by React Native Navigation; called each time a component is revealed to the user. This will be called whenever:

    -   the screen appears - the first time, and also as many times  as the user comes back from a screen pushed over it
    -   the user has moved to another tab and switches back to the tab displaying this screen
    -   a modal is closed which was on top of this screen

and while unmounting the screen:

-   `componentDidDisappear()` Additional method added by React Native Navigation, called each time a component is hidden from the user's view as a result of being detached from hierarchy.
-   `componentWillUnmount()` Clear up references and event listeners here.

#### Lifecycle in functional components

Functional components do not have these lifecycle methods, as the whole function is like one big render function and is executed in one go. However, **hooks** do provide a way to achieve similar capability. `useEffect` is one such hook, which helps perform side-effects in function components.

```javascript { actualFilename=./protected/src/hooks.js endLine=17 startLine=2 statedFilename=someFunctionalComponent.ts url=https&#x3A;//gitlab.com/fullstackio/books/newline-guide-to-react-native-for-javascript-developers/module_02/lesson_01.02/protected/src/hooks.js#L2 }
useEffect(() => {
  // works like `componentDidMount`

  //good place to make that API call
  async function thatAPIcall() {
    
  }
  thatAPIcall();

  // Gets called after every render
  // on mount, and every re-render
  console.log('render!');

  // similar to `componentWillUnmount`, return a function from here
  return () => console.log('unmounting...');
}, []);   // <--- this is very important
```

You will notice that we are passing an `[]` as the second argument to `useEffect` here. This makes the effect behave similarly to how a `componentDidMount` does in a class. The array accepts a list of variables to watch for changes, so an empty array means it is not watching anything, thus no re-renders. If we return a function from this, it will be called when the component is unmounted, working like a `componentWillUnmount`.

We will talk about state management in functional components in detail in [upcoming lessons](state-management-introduction#functional-components-with-hooks).

## Accessing data

While calling any screen, there are three main ways of passing or accessing data. 

-   **Application State `store`** If we have some kind of state management integrated, _redux_ or _mobx_, etc., we can set the data to the application `store` (or `state`). However, a lot of the time, the data that needs to be passed is for once-only use, so this tends to not be the optimum choice.
-   **React Context API**