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Progressive Web Apps, Superpowered
PWA Workshop
Christian Liebel
@christianliebel
Consultant
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Hello, it’s me.
Progressive Web Apps, Superpowered
PWA Workshop
Christian Liebel
Twitter:
@christianliebel
Email:
christian.liebel
@thinktecture.com
Angular & PWA
Slides:
thinktecture.com
/christian-liebel
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And you?
Progressive Web Apps, Superpowered
PWA Workshop
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09:00–10:30 Block 1
10:30–11:00 Break
11:00–12:30 Block 2
12:30–13:30 Lunch Break
13:30–15:00 Block 3
15:00–15:30 Break
15:30–17:00 Block 4
Progressive Web Apps, Superpowered
PWA Workshop
Timetable
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Things NOT to expect
- Blueprint for PWA
development
- No AuthN/AuthZ
Things To Expect
- Extensive/up-to-date insights
into PWA and Project Fugu
- A productivity app use case
that works on your desktop &
smartphone
- Lots of fun
- Hands-on exercises
PWA Workshop
Progressive Web Apps, Superpowered
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https://paint.js.org
– Productivity app
– Draw images
– Lots of actions & tools
– Installable
– Read/save files
– Copy/paste images
from/to clipboard
– Share files to other apps
– Register for file extensions
Progressive Web Apps, Superpowered
PWA Workshop
Demo Use Case
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(Workshop Edition)
– Productivity app
– Draw images
– Lots of actions & tools
– Installable
– Read/save files
– Copy/paste images
from/to clipboard
– Share files to other apps
– Register for file extensions
Progressive Web Apps, Superpowered
PWA Workshop
Demo Use Case
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Setup complete?
(Node.js, Google Chrome, Editor, Git)
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PWA Workshop
Setup (1/3)
LAB #0
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Optional
Download and install Chrome Canary:
https://www.google.com/intl/de/chrome/canary/
Progressive Web Apps, Superpowered
PWA Workshop
Setup (2/3)
LAB #0
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git clone https://github.com/thinktecture/ijs-
munich-2020-pwa.git
cd ijs-munich-2020-pwa
npm i
npm start
Progressive Web Apps, Superpowered
PWA Workshop
Setup (3/3)
LAB #0
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Paint PWA Capabilities
Progressive
Enhancement
Progressive Web Apps, Superpowered
PWA Workshop
Agenda
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Paint PWA Capabilities
Progressive
Enhancement
Progressive Web Apps, Superpowered
PWA Workshop
Agenda
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Canvas
– Plain bitmap for the web
– Cross-platform, hardware-
accelerated graphics
operations
– Supports different contexts
(2D, 3D: WebGL, WebGL 2.0)
– Supported on all evergreen
browsers and on IE 9+
Progressive Web Apps, Superpowered
PWA Workshop
Paint
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Canvas
Add a canvas element to index.html (line 11):
Query the canvas element in app.js (line 1):
const canvas = document.querySelector('#canvas');
Progressive Web Apps, Superpowered
PWA Workshop
Paint
LAB #1
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Canvas 2D Context
fillRect(x, y, width, height)
strokeRect(x, y, width, height)
beginPath()
moveTo(x, y)
lineTo(x, y)
fill()
stroke()
Progressive Web Apps, Superpowered
PWA Workshop
Paint
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Canvas 2D Context
Get the 2D context and prepare the canvas in app.js:
const canvas = document.querySelector('#canvas');
const ctx = canvas.getContext('2d');
ctx.fillStyle = 'white';
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.fillStyle = 'black';
Progressive Web Apps, Superpowered
PWA Workshop
Paint
LAB #2
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Low-latency Rendering
Progressive Web Apps, Superpowered
PWA Workshop
Paint
Web pages need to synchronize
with the DOM on graphics updates
causing latencies that can make
drawing difficult
Low-latency rendering skips
syncing with the DOM with can lead
to a more natural experience
Supported on Chrome (Chrome OS
and Windows only)
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Low-latency Rendering
Opt-in to low-latency rendering (app.js):
const ctx = canvas.getContext('2d', {
desynchronized: true
});
Progressive Web Apps, Superpowered
PWA Workshop
Paint
LAB #3
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Pointer Events
Progressive Web Apps, Superpowered
PWA Workshop
Paint
Users nowadays use different
input methods, cross-platform
apps should cover all of them
Pointer Events offer an
abstract interface to catch all
input methods (pointerdown,
pointermove, pointerup)
event.offsetX/event.offsetY
contain the pointer’s position
relative to the listener
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Pointer Events
Add event listeners (bottom of app.js):
canvas.addEventListener('pointerdown', event => {});
canvas.addEventListener('pointermove', event => {
// ~~ is the shorter Math.floor()
ctx.fillRect(~~event.offsetX, ~~event.offsetY, 2, 2);
});
canvas.addEventListener('pointerup', () => {});
Progressive Web Apps, Superpowered
PWA Workshop
Paint
LAB #4
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Bresenham Line Algorithm
The user may move faster than
the input can be processed
For this case, we need to
remember the previous point
and interpolate the points in
between
The Bresenham line algorithm
calculates the missing pixels
between two given points
Progressive Web Apps, Superpowered
PWA Workshop
Paint
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Bresenham Line Algorithm
1. Add the following import to the top of app.js (“.js” is required, otherwise the request will 404):
import {bresenhamLine} from "./helpers.js";
2. Then, adjust the event listeners:
a) In the pointerdown event handler, store ~~event.offsetX/~~event.offsetY in a variable
called previousPoint (~~ is required, otherwise Bresenham will go into an endless loop)
b) In pointermove
i. only draw if the pointer is down
ii. retrieve the current point (event.offsetX|Y, ~~ required!)
iii. In a for…of loop, call bresenhamLine() with previousPoint.x|y & currentPoint.x|y and
draw a 2x2 rectangle for each returned point.
iv. store current point in previousPoint
c) In pointerup, set previousPoint to null again.
Progressive Web Apps, Superpowered
PWA Workshop
Paint
LAB #5
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Bresenham Line Algorithm
let previousPoint = null;
canvas.addEventListener('pointerdown', event => previousPoint = {x: ~~event.offsetX,
y: ~~event.offsetY});
canvas.addEventListener('pointermove', event => {
if (previousPoint) {
const currentPoint = {x: ~~event.offsetX, y: ~~event.offsetY};
for(let {x, y} of bresenhamLine(previousPoint.x, previousPoint.y,
currentPoint.x, currentPoint.y)) {
ctx.fillRect(x, y, 2, 2);
}
previousPoint = currentPoint;
}
});
canvas.addEventListener('pointerup', () => previousPoint = null);
Progressive Web Apps, Superpowered
PWA Workshop
Paint
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Color Selection
For this demo, we will only
implement the brush tool. However,
we want to bring in some color.
A simple method to implement a
color selection is to use the HTML
color-type input element that
shows the native color picker:
Progressive Web Apps, Superpowered
PWA Workshop
Paint
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Color Selection
1. In index.html, add the following input to the node:
2. In app.js, add the following code at the bottom:
const txtColor = document.querySelector('#color');
txtColor.addEventListener('change', () => {
ctx.fillStyle = txtColor.value;
});
Progressive Web Apps, Superpowered
PWA Workshop
Paint
LAB #6
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Paint PWA Capabilities
Progressive
Enhancement
Progressive Web Apps, Superpowered
PWA Workshop
Agenda
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PWA Workshop
Progressive Web Apps, Superpowered
Responsive Linkable Discoverable Installable App-like
Connectivity
Independent
Fresh Safe Re-engageable Progressive
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Progressive Web Apps, Superpowered
PWA Workshop
Web App
Manifest
Service
Worker
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Web App Manifest
Distinguishes Web Apps from
Websites
JSON-based file containing
metadata for apps only
Apps can be identified by search
engines, app store providers, etc.
Progressive Web Apps, Superpowered
PWA Workshop
PWA
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manifest.webmanifest
{
"short_name": "Paint",
"name": "Paint Workshop",
"theme_color": "white",
"icons": [{
"src": "icon.png",
"sizes": "512x512"
}],
"start_url": "/index.html",
"display": "standalone",
"shortcuts": [/* … */]
}
Progressive Web Apps, Superpowered
PWA Workshop
PWA
Names
Icons
Display Mode
Shortcuts
Start URL
Theme color (status bar/window bar)
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Manifest Display Modes
Progressive Web Apps, Superpowered
PWA Workshop
PWA
browser minimal-ui standalone fullscreen
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Manifest Icon Purposes
(any)
any context (e.g. app icon)
monochrome
different color requirements
(at risk)
maskable
user agent masks icon as required
Progressive Web Apps, Superpowered
PWA Workshop
PWA
Safe Zone
Windows iOS Android
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Web App Manifest
1. In index.html, add the following tag to the document’s node (e.g., after the
stylesheet):
2. Create the new file manifest.webmanifest and set:
a) name and short_name to values of your choice
b) display to standalone
c) theme_color to #000080 and background_color to #808080
d) start_url to /index.html and scope to /
e) icons to [{ src: "icon.png", sizes: "512x512" }]
3. Test manifest in DevTools: F12 > Application > Manifest
Progressive Web Apps, Superpowered
PWA Workshop
PWA
LAB #7
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Manifest Shortcuts
Progressive Web Apps, Superpowered
PWA Workshop
PWA
Secondary entrypoints for your
application (e.g., home screen
quick actions, jump lists, …)
Static definition in Web App
Manifest
Dynamic API may follow in the
future
Supported by Google Chrome
for Android
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Web App Manifest
1. In manifest.webmanifest, add (at least) the following shortcut:
"shortcuts": [{
"name": "About Paint",
"short_name": "About",
"description": "Show information about Paint",
"url": "/about.html",
"icons": [{ "src": "icon.png", "sizes": "512x512" }]
}],
2. Test in DevTools: F12 > Application > Manifest
Progressive Web Apps, Superpowered
PWA Workshop
PWA
LAB #8
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Web App Manifest – Chrome Installability Signals
Web App is not already installed
Meets a user engagement heuristic (previously: user has interacted with
domain for at least 30 seconds)
Includes a Web App Manifest that has short_name or name, at least a
192px and 512px icon, a start_url and a display mode of fullscreen,
standalone or minimal-ui
Served over HTTPS
Has a registered service worker with a fetch event handler
Progressive Web Apps, Superpowered
PWA Workshop
PWA
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Service Worker
JavaScript snippet executed in an
own thread, registered by the website
Acts as a controller, proxy, or
interceptor
Has a cache to store responses (for
offline availability and performance)
Can wake up even when the website
is closed and perform background
tasks (e.g., push notifications or sync)
Progressive Web Apps, Superpowered
PWA Workshop
PWA
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Service Worker
Progressive Web Apps, Superpowered
PWA Workshop
PWA
Service
Worker
Internet
Website
HTML/JS
Cache
fetch
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Workbox
Toolchain by Google
Includes a CLI
Generates a service worker
implementation from directory
contents (e.g., build output, or
our development directory)
Allows you to modify the
service worker behavior
(maximum flexibility)
Progressive Web Apps, Superpowered
PWA Workshop
PWA
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Service Worker
1. In your console, run:
a) npm run workbox wizard (use “src” as project root and defaults for the rest)
b) npm run workbox generateSW
2. In index.html, add the following script to the bottom of the node:
if (navigator.serviceWorker) {
navigator.serviceWorker.register('sw.js');
}
3. Test in DevTools: F12 > Application > Service Worker
4. Install the app: Address Bar > ⊕ Install
Progressive Web Apps, Superpowered
PWA Workshop
PWA
LAB #9
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Service Worker Debugging
More information on installed
service workers can be found on
• chrome://serviceworker-
internals (Google Chrome)
• about:serviceworkers
(Mozilla Firefox)
Progressive Web Apps, Superpowered
PWA Workshop
PWA
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Service Worker Debugging
Progressive Web Apps, Superpowered
PWA Workshop
PWA
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Lighthouse
Progressive Web Apps, Superpowered
PWA Workshop
PWA
Auditing tool by Google,
integrated in Chrome DevTools
Automatically checks
performance metrics, PWA
support, accessibility, SEO and
other best practices and gives
tips on how to improve
Can simulate mobile devices
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Lighthouse
1. Make sure only one tab/window of your PWA is open
2. Open DevTools: F12 > Lighthouse
3. Make sure to select at least the “Progressive Web App” category
4. Click “Generate report”
Progressive Web Apps, Superpowered
PWA Workshop
PWA
LAB #10
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Paint PWA Capabilities
Progressive
Enhancement
Progressive Web Apps, Superpowered
PWA Workshop
Agenda
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Progressive Web Apps, Superpowered
PWA Workshop
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Project Fugu
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
»Let’s bring the web
back – API by API«
Thomas Steiner, Google
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Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
Contacts
Picker
Screen Wake
Lock API
File System
Access API
Shape
Detection API
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Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
https://goo.gle/fugu-api-tracker
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Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
navigator.share({ url: 'http://example.com' });
ShareIntent DataTransferManager
…
NSSharingServicePicker
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File System Access API
Some applications heavily rely
on working with files (e.g.
Visual Studio Code, Adobe
Photoshop, …)
File System Access API allows
you to open, save and override
files and directories
Shipped with Google Chrome
86
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
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File System Access API
1. Add the following buttons to the bar in index.html (before the color input):
Open
Save
Copy
Paste
Share
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
LAB #11
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File System Access API
2. At the top of app.js, change the import as follows:
import {bresenhamLine, getImage, toBlob} from "./helpers.js";
3. Add the following lines at the bottom of app.js:
const fileOptions = {
types: [{
description: 'PNG files',
accept: {'image/png': ['.png']}
}]
};
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
LAB #11
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File System Access API
4. Add the following lines at the bottom of app.js:
const btnSave = document.querySelector('#save');
btnSave.addEventListener('click', async () => {
const blob = await toBlob(canvas);
const handle = await window.showSaveFilePicker(fileOptions);
const writable = await handle.createWritable();
await writable.write(blob);
await writable.close();
});
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
LAB #11
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File System Access API
Add the following code at the end of app.js:
const btnOpen = document.querySelector('#open');
btnOpen.addEventListener('click', async () => {
const [handle] = await window.showOpenFilePicker(fileOptions);
const file = await handle.getFile();
const image = await getImage(file);
ctx.drawImage(image, 0, 0);
});
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
LAB #12
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Async Clipboard API
Allows reading from/writing to
the clipboard in an
asynchronous manner (UI won’t
freeze during long-running
operations)
Reading from the clipboard
requires user consent first
(privacy!)
Supported by Chrome, Edge
and Safari
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
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Async Clipboard API
Add the following code at the end of app.js:
const btnCopy = document.querySelector('#copy');
btnCopy.addEventListener('click', async () => {
const blob = await toBlob(canvas);
await navigator.clipboard.write([
new ClipboardItem({[blob.type]: blob})
]);
});
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
LAB #13
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Async Clipboard API
const btnPaste = document.querySelector('#paste');
btnPaste.addEventListener('click', async () => {
const clipboardItems = await navigator.clipboard.read();
for (const clipboardItem of clipboardItems) {
for (const type of clipboardItem.types) {
if (type === 'image/png') {
const blob = await clipboardItem.getType(type);
const image = await getImage(blob);
ctx.drawImage(image, 0, 0);
}
}
}
});
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
LAB #14
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Web Share API
Allows sharing a title, URL, text, or
files
API can only be invoked as a
result of a user action (i.e. a click
or keypress)
Files supported in Chrome on
Android, Edge on Windows
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
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Web Share API
const btnShare = document.querySelector('#share');
btnShare.disabled = !('canShare' in navigator);
btnShare.addEventListener('click', async () => {
const blob = await toBlob(canvas);
const file = new File([blob], 'untitled.png', {type: 'image/png'});
const item = {files: [file], title: 'untitled.png'};
if (await navigator.canShare(item)) {
await navigator.share(item);
}
});
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
LAB #15
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File System Handling API
Register your PWA as a
handler for file extensions
Requires installing the
application first
Declare supported extensions
in Web App Manifest and add
imperative code to your
application logic
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
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File System Handling API
1. Enable the following flag in Chrome Canary and restart the browser:
chrome://flags/#file-handling-api
2. Add the following property to your manifest (manifest.webmanifest):
"file_handlers": [{
"action": "/index.html",
"accept": {
"image/png": [".png"]
}
}]
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
LAB #16
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File System Handling API
3. Add the following code to the bottom of app.js:
if ('launchQueue' in window) {
launchQueue.setConsumer(async params => {
const [handle] = params.files;
if (handle) {
const file = await handle.getFile();
const image = await getImage(file);
ctx.drawImage(image, 0, 0);
}
});
}
4. Re-generate Service Worker: npm run workbox generateSW
Progressive Web Apps, Superpowered
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Capabilities
LAB #16
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Summary
- Project Fugu helps the web to become more and more capable
- Project Fugu APIs could bring many more app experiences to the web
(IDEs, productivity apps, etc.)
- But: Web is threatened by alternative approaches and platforms,
support for modern Web API varies from platform to platform
- You can make a difference!
- File bugs in browser engine bugtrackers
- File Fugu requests: https://goo.gle/new-fugu-request
Progressive Web Apps, Superpowered
PWA Workshop
Capabilities
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Paint PWA Capabilities
Progressive
Enhancement
Progressive Web Apps, Superpowered
PWA Workshop
Agenda
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Overview
Use available interfaces and functions of
a system (opposite of Graceful
Degradation)
Users with modern, feature-rich
browsers get a better experience
Apps are available on older browsers, but
with limited functionality
Concept: Browser feature support should
grow over time—thereby more users can
enjoy an increasing number of features
Progressive Web Apps, Superpowered
PWA Workshop
Progressive Enhancement
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Overview
if ('serviceWorker' in navigator) {
navigator.serviceWorker.register(…)
.then(() => /* … */);
}
In JavaScript: check whether an API/feature is available. If yes—use it!
Otherwise:
1. Disable the functionality
2. Fall back to an alternative API (if available)
Progressive Web Apps, Superpowered
PWA Workshop
Progressive Enhancement
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Disabling unsupported features
In app.js, disable the buttons in case the respective API does not exist, e.g.:
btnOpen.disabled = !('showOpenFilePicker' in window);
1. Open: window.showOpenFilePicker()
2. Save: window.showSaveFilePicker()
3. Copy: navigator.clipboard + navigator.clipboard.read()
4. Paste: navigator.clipboard + navigator.clipboard.write()
5. Share: navigator.canShare()
Progressive Web Apps, Superpowered
PWA Workshop
Progressive Enhancement
LAB #17
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Providing an alternative implementation
1. In app.js, test for the existence of the showSaveFilePicker() method
on the navigator object.
2. If the method does not exist, fall back to the following code for save:
const anchor = document.createElement('a');
const url = URL.createObjectURL(blob);
anchor.href = url;
anchor.download = '';
anchor.click();
URL.revokeObjectURL(url);
Progressive Web Apps, Superpowered
PWA Workshop
Progressive Enhancement
LAB #18
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Deployment
Progressive Web Apps, Superpowered
PWA Workshop
Electron/Capacitor
JS
HTML
CSS
.ipa
.exe .app ELF
.apk .appx
Single-Page
Application
Capacitor
Electron
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(Simplified)
Progressive Web Apps, Superpowered
PWA Workshop
Store Deployments
https://example.com
.appx
.apk
Server
Microsoft
Store
Play
Store
Source
Files
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Run app on your device
https://ngrok.com/download
ngrok http 3000
Progressive Web Apps, Superpowered
PWA Workshop
LAB #19
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Crunch Time
Progressive Web Apps, Superpowered
PWA Workshop
LAB #20
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Q&A
Progressive Web Apps, Superpowered
PWA Workshop
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New powerful APIs regularly ship with new releases of Chromium-based
browsers
Some only add minor finishing touches, others enable whole application
categories as productivity apps to finally make the shift to the web
Some APIs already made their way into other browsers (e.g., Web Share)
Fugu process makes sure that capabilities are implemented in a secure,
privacy-preserving manner
Let’s make the web a more capable platform!
Progressive Web Apps, Superpowered
PWA Workshop
Summary
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Thank you
for your kind attention!
Christian Liebel
@christianliebel
[email protected]