React Native Evening

ReactNative Evening
CoWork South Bay
Torrance, CA
26 July 2017
@ 7:00 PM, PDT

Me
• Troy Miles
• Over 38 years of programming
experience
• Software engineer, speaker,
book and video author
• rockncoder@gmail.com
• @therockncoder
• lynda.com Author

“Learn once, write anywhere: Build mobile apps
with React”

React Native
• “Deliver native Android, iOS, and Windows apps,
using existing skills, teams, and code.”
• Released: March 27, 2015
• 51k+ GitHub Stars

Installation
• Node.js (& npm)
• Android SDK
• iOS SDK (on Mac only)
• React Native

Android Development
• Install Java 8
• Install Android Studio
• Install Android SDK 23 (Marshmallow)
• Install Intel HAXM (x86 Android Emulator)

iOS Development
• Install Xcode from macOS App Store

Mac Installation
• brew install node
• brew install watchman*
• npm i -g react-native-cli

Windows Installation
• choco install nodejs.install
• choco install python2
• choco install jdk8

iOS Development
• In order to build apps for iOS you must have a Mac

React-Native
• react-native init <app name>
• cd <app name>
• react-native run-android / run-ios

react-native CLI
Command Purpose
init [app name] creates a react-native app
run-android [options] builds app, starts on Android
run-ios [options] builds app, starts on iOS
start [options] starts webserver
new-library [options] generates a native library bridge
bundle [options] builds ofﬂine javascript bundle
unbundle [options] builds unbundle javascript

react-native CLI
Command Purpose
eject [options] takes the shackles off
link [options] <packageName> links all native dependencies
unlink [options] <packageName> unlink native dependency
install [options] <packageName> install+link native dependencies
uninstall [options] <packageName> uninstall+unlink native
upgrade [options] upgrade app's template ﬁles
log-android [options] starts adb logcat
log-ios [options] starts iOS device syslog tail

Application Root Directory
• All of the commands, for all of the tools are
designed work on the application root directory
• If used anywhere else bad things will happen
• be sure you are in the app root
• double check that you are in the app root

ECMAScript Versions
Version Date
ES1 June 1997
ES2 June 1998
ES3 December 1999
ES4 DOA 2006
ES5 December 2009
ES2015 / ES6 June 2015
ES2016 / ES7 2016

Collection Operators
• .isArray()
• .every()
• .forEach()
• .indexOf()
• .lastIndexOf()
• .some()
• .map()
• .reduce()
• .ﬁlter()

map
let junk = [1, 2, 3, 4, 'Alpha', 5, {name: 'Jason'}]; 
let letters = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K']; 
let nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]; 
console.log(nums); 
 
// map iterates over all of the elements and returns a new array with the same
// number of elements 
let nums2 = nums.map((elem) => elem * 2); 
console.log(nums2);
/// [2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40]

ﬁlter
let nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]; 
 
// filter iterates over the array and returns a new array with only the elements
// that pass the test 
let nums3 = nums.filter((elem) => !!(elem % 2)); 
console.log(nums3);
/// [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

reduce
let nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]; 
 
// reduce iterates over the array passing the previous value and the current 
// element it is up to you what the reduction does, let's concatenate the strings 
let letters2 = letters.reduce((previous, current) => previous + current); 
console.log(letters2);
/// ABCDEFGHIJK 
 
// reduceRight does the same but goes from right to left 
let letters3 = letters.reduceRight((previous, current) => previous + current); 
console.log(letters3);
/// KJIHGFEDCBA

let
• let allows us to create a block scoped variables
• they live and die within their curly braces
• var is considered deprecated
• best practice is to use let instead of var

let
// let allows us to create block scoped variables 
// they live and die within the curly braces 
let val = 2; 
console.info(`val = ${val}`); 
{ 
let val = 59; 
console.info(`val = ${val}`); 
} 
console.info(`val = ${val}`);

const
• const creates a variable that can't be changed
• best practice is to make any variable that should
not change a constant
• does not apply to object properties or array
elements

const
const name = 'Troy'; 
console.info(`My name is ${name}`); 
// the line below triggers a type error 
name = 'Miles';

Template strings
• Deﬁned by using opening & closing back ticks
• Templates deﬁned by ${JavaScript value}
• The value can be any simple JavaScript expression
• Allows multi-line strings (return is pass thru)

Template strings
let state = 'California'; 
let city = 'Long Beach'; 
console.info(`This weekend's workshop is in ${city}, ${state}.`); 
 
// template strings can run simple expressions like addition 
let cup_coffee = 4.5; 
let cup_tea = 2.5; 
console.info(`coffee: $${cup_coffee} + tea: $${cup_tea} = $$
{cup_coffee + cup_tea}.`); 
 
// they can allow us to create multi-line strings 
console.info(`This is line #1. 
this is line #2.`);

Arrow functions
• Succinct syntax
• Doesn’t bind its own this, arguments, or super
• Facilitate a more functional style of coding
• Can’t be used as constructors

Arrow functions
• When only one parameter, parenthesis optional
• When zero or more than one parameter,
parenthesis required

Arrow function
let anon_func = function (num1, num2) { 
return num1 + num2; 
}; 
console.info(`Anonymous func: ${anon_func(1, 2)}`); 
 
let arrow_func = (num1, num2) => num1 + num2; 
console.info(`Arrow func: ${arrow_func(3, 4)}`);

this
• this is handled different in arrow functions
• In anonymous function this is bound to the global
object
• In arrow function this is what it was in the outer
scope

Destructuring
• Maps the data on the right side of the equals sign
to the variables on the left
• The data type decides the way values are mapped
• It is either object or array destructuring

Object Destructuring
16// this is a demo of the power of destructuring
17// we have two objects with the same 3 properties
18 const binary = {kb: 1024, mb: 1048576, gb: 1073741824};
19 const digital = {kb: 1000, mb: 1000000, gb: 1000000000};
20// We use a ternary statement to choose which object
21// assign properties based on their property names
22 const {kb, mb, gb} = (useBinary) ? binary : digital;

Array Destructuring
5
6 let [param1, bob, key] = ['first', 'second', '3rd'];
7 console.info(`param1 = ${param1}, bob = ${bob}, key = ${key}`);
8 // param1 = first, bob = second, key = 3rd

Spread syntax
• Expands an expression in places where multiple
arguments, elements, or variables are expected

The spread operator
11
12 // the spread operator
13 const myArray = ['Bob', 'Sue', 'Fido'];
14 function printFamily(person1, person2, pet) {
15 console.info(`Person 1: ${person1}, Person 2: ${person2}, and their pet: ${pet}`);
16 }
17 printFamily(...myArray);
18 // Person 1: Bob, Person 2: Sue, and their pet: Fido
19

Class
• Syntactic sugar over JavaScript use of function
constructors
• JavaScript uses proto-typical inheritance
• If a class extends another, it must include super()
as ﬁrst instruction in its constructor
• Only create a constructor if it does something

import
• Imports functions, objects, or primitives from other
ﬁles
• import <name> from “<module name>”;
• import {name } from “<module name>”;
• import * as Greetings from “<module name>”;
• relative path indicates not an npm package

export
• export <var a>
• export {a, b};

export default
• only one per ﬁle
• common pattern for libraries
• const Greetings = {sayHi, sayBye};
• export default Greetings;
• export default {sayHi, sayBye};

Importing Old School JS
• Many JS libraries don’t support the new syntax
• How do we use them?
• import ‘jquery’;

React
• A JavaScript library for building user interfaces
• Created by Facebook & Instagram
• Initial release March 2013
• Current version 15.6.1
• Next major version 16.0.0, will have breaking
changes

React
• Virtual DOM
• One-way data ﬂow
• JSX - JavaScript eXtension allows in HTML
generation
• Component-based

React API
• The use of JSX is optional in React
• You can use the React “API” instead
• The createClass method is deprecated and will be
removed in React 16

Component
• Fundamental building block of React
• Can be created with a JS Class or Function
• The render method is mandatory

Class Component
3
4 class Square extends React.Component {
5 render() {
6 return (
7 <button
8 className="square"
9 onClick={() => this.props.onClick()}>
10 {this.props.value}
11 </button>
12 );
13 }
14 }
15

Functional Component
15
16 function Square(props) {
17 return (
18 <button
19 className="square"
20 onClick={() => props.onClick()}>
21 {props.value}
22 </button>
23 );
24 }

React.PropTypes
• React.PropTypes is deprecated
• It will be deleted in React 16
• Use the npm package “prop-types” instead
• import PropTypes from ‘prop-types’;

PropTypes
• PropTypes allow you to declare what properties
your component expects
• React validates property at runtime
• Using propTypes is optional

Some PropTypes
Component Command
PropTypes.array an optional array
PropTypes.bool an optional bool
PropTypes.element An optional React element
PropTypes.func An optional function
PropTypes.node Anything that can be rendered
PropTypes.number An optional number
PropTypes.object An optional object
PropTypes.string An optional string
PropTypes.symbol An optional Symbol

PropType in code
1
2 import React from 'react';
3 import ReactDOM from 'react-dom';
4 import PropTypes from 'prop-types';
5
6 class App extends React.Component {
7 render () {
8 return React.DOM.span(null, `My name is ${this.props.name}`);
9 }
10 }
11
12 App.propTypes = {
13 name: PropTypes.string.isRequired
14 };
15
16 ReactDOM.render(
17 React.createElement(App, {}),
18 document.getElementById('root')
19 );
20
21

React Components
• Can be created two ways:
• Using JavaScript
• Using JSX

Components via JS
• React’s API contains method createElement()
• Takes 3 parameters: type, props, children
render() {
return React.createElement('h1', null, "Hello there.");

JSX
• JavaScript Syntax EXtension
• A mixture of JavaScript and HTML syntax
• Compiles to JavaScript
• Is optional but preferred over using JavaScript
• Is easier to read

JSX Attributes
• Can assign either a string or an expression
• Strings can be either single or double quotes
• Expressions must be enclosed with curly braces

Boolean Attributes
• HTML has a few boolean attributes, if present they
are true
• Some of these include: checked, selected,
disabled
• In JSX,
• <Component disabled={true / false} />

Forbidden Attributes
• Two attributes are JavaScript keywords
• JavaScript keywords can’t be used in JSX
• class -> className
• for -> htmlFor

JSX Spread Syntax
• a shortcut to passing props to a component
• uses ES2015 spread operator
• <Component {…object} />

JSX Spread Syntax
return (
<Timer
id={this.props.id}
amount={this.props.amount}
elapsed={this.props.elapsed}
runningSince={this.props.runningSince}
onStartClick={this.props.onStartClick}
onStopClick={this.props.onStopClick}
onResetClick={this.props.onResetClick}
onSetClick={this.handleSetClick}
/>
);

JSX Spread Syntax
return (
<Timer
{...this.props}
/>
);

JSX Debugging Tip
• Assign component to a variable
• console.log the variable

JSX Debugging Tip
const timerComp = (
<Timer troy='miles'
{...this.props}
/>
);
console.log(timerComp);

Lifecycle Events
Event When
componentWillMount invoked once before rendering
componentDidMount invoked after component loaded
componentWillReceiveProps invoked when receiving new props
shouldComponentUpdate asks if component should update
componentWillUpdate invoked before rendering new props
componentDidUpdate invoked after rendered new props
componentWillUnmount invoked before component removed

System Components
Component
ActivityIndicator
Button
DatePickerIOS
DrawerLayoutAndroid
FlatList
Image
KeyboardAvoidingView

System Components
Component
ListView
Modal
NavigatorIOS
Picker
PickerIOS
ProgressBarAndroid
ProgressViewIOS

System Components
Component
RefreshControl
ScrollView
SectionList
SegmentedControlIOS
Slider
SnapshotViewIOS
StatusBar

System Components
Component
Switch
TabBarIOS
TabBarIOS.Item
Text
TextInput
ToolbarAndroid
TouchableHighlight

System Components
Component
TouchableNativeFeedback
TouchableOpacity
TouchableWithoutFeedback
View
ViewPagerAndroid
VirtualizedList
WebViewAPIs

Platform Differences
• Not all components work with all devices
• Some are for iOS only or Android only
• Those that end in IOS are for iOS
• Those that end in Android are for Android

Summary
• React Native allows you to make mobile apps in JS
• While easier than native development, it is not easy

React Native Evening

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