Crossing platforms with JavaScript & React

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@robdel12

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JavaScript is EVERYWHERE

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Web

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Server

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iOS

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Android

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Desktop

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What is cross platform JS?

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JS that can run on more than one platform

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“Why did the iOS team implement it like this?”

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“The Android app currently doesn’t support that”

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https://twitter.com/dan_abramov/status/812047645732651009

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Easier to share code across many teams

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More team collaboration since there’s more overlap

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It allows teams to own products & not be separated by technology

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TL;DR your team now owns the iOS, Android, and (maybe) web apps.

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Consistency is

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Cheaper

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If you can build iOS & Android apps in the same code base it should be cheaper

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Why not bet on the web?

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Native will be better than mobile web for a while

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Why not take the web tooling & get native results?

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You are betting on the web

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Can’t beat them, join them

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I decided to be ambitious

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Build an Instagram clone for Web, iOS, & Android

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Why an Instagram clone?

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Use Impagination.js to power an Inﬁnite scroll of images

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Impagination will work on any JS codebase

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Building inﬁnite scroll in React Native with Impagination http://bit.ly/reactnativeinﬁnitescroll

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We’ve already used Impagination in four different platforms

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What else can be shared?

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Experiment time

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Three phases to the experiment • Planning • Implementation • Postmortem

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Planning

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The stack • React Native • React (DOM) • Auth0 (authentication) • Graph.cool (backend) • Impagination (inﬁnite datasets)

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What should the app do? • Login / Sign up • See your proﬁle & images you’ve posted • Edit your proﬁle • Post a new photo • Main list feed showing everyones posts

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Web demo

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Implementation

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What’s the approach?

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Build the web app

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Start to build the native app

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Realize I’ve already solved these problems in the web app

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Refactor

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ListPage.js

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ListPage.js handles both UI & data right now

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ListPage for native duplicates a lot form web ListPage

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class ListPage extends React.Component { static propTypes = { data: React.PropTypes.object, } state = { dataset: null, datasetState: null, } setupImpagination() {} componentWillMount() {this.setupImpagination();} setCurrentReadOffset = (event) => {} render () { return (

{this.state.datasetState.map(record => { if (record.isPending && !record.isSettled) { return ; } return ; })}

); } } const FeedQuery = gql`query($skip: Int!, $first: Int!) { allPhotos(orderBy: createdAt_DESC, first: $first, skip: $skip) { } }`; export default graphql(FeedQuery, {options: {variables: { skip: 0, first: PAGE_SIZE }}})(ListPage); Web ListPage.js

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` class ListPage extends React.Component { static propTypes = { data: React.PropTypes.object, } state = { dataset: null, datasetState: null, } setupImpagination() {} componentWillMount() {this.setupImpagination();} setCurrentReadOffset = (event) => {} render () { return ( {this.state.datasetState.map(record => { if(record.isPending && !record.isSettled) { return ; } return ; })} ); } } const FeedQuery = gql`query($skip: Int!, $first: Int!) { allPhotos(orderBy: createdAt_DESC, first: $first, skip: $skip) { } }`; export default graphql(FeedQuery, {options: {variables: { skip: 0, first: PAGE_SIZE }}})(ListPage); Native ListPage.js

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Everything but the UI is the same

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New structure

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Presentation & container components

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import ListPageView from ‘../components/presentational/ListPageView’; class ListPageContainer extends React.Component { state = { dataset: null, datasetState: null, } setupImpagination() {} componentWillMount() {this.setupImpagination();} setCurrentReadOffset = (event) => {} render () { return ( ; ); } } const FeedQuery = gql`query($skip: Int!, $first: Int!) { allPhotos(orderBy: createdAt_DESC, first: $first, skip: $skip) { } }`; export default graphql(FeedQuery, {options: {variables: { skip: 0, first: PAGE_SIZE }}})(ListPage);

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Make the container component render a separate presentation component

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Leave setting the readOffset to the presentation components

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setCurrentReadOffset function is passed as a prop from the container component

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t import React, { Component } from 'react'; import Infinite from 'react-infinite'; import Photo from '../presentational/Photo'; import LoadingPost from '../presentational/LoadingPost'; const ITEM_HEIGHT = 600; const HEADER_HEIGHT = 80; class ListPageView extends Component { setCurrentReadOffset = (event) => { let currentItemIndex = Math.ceil((window.scrollY - HEADER_HEIGHT) / ITEM_HEIGHT); this.props.setCurrentReadOffset(currentItemIndex); } render() { return (

{this.props.datasetState.map(record => { if (record.isPending && !record.isSettled) { return ; } return ; })}

); } } export default ListPageView; Web presentation component

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Native presentation component import React, { Component } from 'react'; import Photo from '../presentational/Photo'; import LoadingPost from '../presentational/LoadingPost'; import { ScrollView } from 'react-native'; const ITEM_HEIGHT = 485; class ListPageView extends Component { setCurrentReadOffset = (event) => { let currentOffset = Math.floor(event.nativeEvent.contentOffset.y); let currentItemIndex = Math.ceil(currentOffset / ITEM_HEIGHT); this.props.setCurrentReadOffset(currentItemIndex); } render() { return ( {this.props.datasetState.map(record => { if(record.isPending && !record.isSettled) { return ; } return ; })} ); } } export default ListPageView;

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This theme continues throughout the entire app

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} />

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Native app demo

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Postmortem

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Building the apps in time was hard…

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Figuring out what code is shareable

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Figuring out how to make that code shareable

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React Router is neat & works cross platform There are different imports for React Native & React

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Auth0 was very easy to implement on both platforms. There are different APIs for React Native & React

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AsyncStorage vs localStorage

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What all ended up being shared?

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✅ List feed ✅ User proﬁle ✅ Edit user proﬁle ✅ Sign up ✅ New post

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Beyond login mostly everything else is the same

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The UI changed but not the business logic

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Key takeaways

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We’re in a post DOM world

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Write JavaScript interaction models

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The UI framework will change but the underlying model driving it won’t

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“It’s just JavaScript”

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We get stronger libraries by increasing the number of users & contributors.

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React makes this very easy thanks to React & React Native

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I was able to share the same ﬁve container components across three different platforms

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Write one container component and many UI components

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The core of this app is shared

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That’s a cost savings

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I own this entire product & its 3 platforms

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In 2 weeks I was able do all of this

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Cross platform JS FTW

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Instagram also agrees with me https://engineering.instagram.com/react-native-at-instagram- dd828a9a90c7#.i364vchox