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PWA Bootcamp
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Christian Liebel
@christianliebel
Consultant
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Hello, it’s me.
PWA Bootcamp
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Christian Liebel
Twitter:
@christianliebel
Email:
christian.liebel
@thinktecture.com
Angular & PWA
Slides:
thinktecture.com
/christian-liebel
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13:30–15:00 Block 1
15:00–15:30 Break
15:30–17:00 Block 2
PWA Bootcamp
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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
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PWA Bootcamp
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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
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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
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Demo Use Case
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Setup complete?
(Node.js, Google Chrome, Editor, Git)
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Setup (1/3)
LAB
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Optional
Download and install Chrome Canary:
https://www.google.com/intl/de/chrome/canary/
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Setup (2/3)
LAB
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git clone https://github.com/thinktecture/
mobiletechcon-2020-pwa.git
cd mobiletechcon-2020-pwa
npm i
npm start
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Setup (3/3)
LAB
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Paint PWA Capabilities
Progressive
Enhancement
PWA Bootcamp
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Agenda
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Paint PWA Capabilities
Progressive
Enhancement
PWA Bootcamp
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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+
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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');
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Paint
LAB
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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()
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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';
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Paint
LAB
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Low-latency Rendering
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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
});
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Paint
LAB
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Pointer Events
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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', () => {});
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Paint
LAB
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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
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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:
let previousPoint = null;
canvas.addEventListener('pointerdown', event => {
previousPoint = { x: ~~event.offsetX, y: ~~event.offsetY };
});
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Paint
LAB
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Bresenham Line Algorithm
canvas.addEventListener('pointermove', event => {
if (previousPoint) {
const currentPoint = { x: ~~event.offsetX, y: ~~event.offsetY };
for(const point of bresenhamLine(previousPoint.x, previousPoint.y,
currentPoint.x, currentPoint.y)) {
ctx.fillRect(point.x, point.y, 2, 2);
}
previousPoint = currentPoint;
}
});
canvas.addEventListener('pointerup', () => {
previousPoint = null;
});
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Paint
LAB
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Paint PWA Capabilities
Progressive
Enhancement
PWA Bootcamp
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Agenda
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PWA Bootcamp
Responsive Linkable Discoverable Installable App-like
Connectivity
Independent
Fresh Safe Re-engageable Progressive
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PWA Bootcamp
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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.
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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": [/* … */]
}
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PWA
Names
Icons
Display Mode
Shortcuts
Start URL
Theme color (status bar/window bar)
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Manifest Display Modes
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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
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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
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PWA
LAB
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Manifest Shortcuts
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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 – 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
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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)
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PWA
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Service Worker
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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)
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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
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PWA
LAB
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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)
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PWA
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Service Worker Debugging
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PWA
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Lighthouse
PWA Bootcamp
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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”
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PWA
LAB
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Paint PWA Capabilities
Progressive
Enhancement
PWA Bootcamp
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Agenda
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PWA Bootcamp
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Project Fugu
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Capabilities
»Let’s bring the web
back – API by API«
Thomas Steiner, Google
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Capabilities
Contacts
Picker
Screen Wake
Lock API
File System
Access API
Shape
Detection API
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PWA Bootcamp
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Capabilities
https://goo.gle/fugu-api-tracker
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PWA Bootcamp
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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
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Capabilities
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File System Access API
1. Add the following buttons to the bar in index.html:
Open
Save
Copy
Paste
Share
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Capabilities
LAB
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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']}
}]
};
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Capabilities
LAB
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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();
});
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Capabilities
LAB
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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);
});
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Capabilities
LAB
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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
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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})
]);
});
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Capabilities
LAB
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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);
}
}
}
});
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Capabilities
LAB
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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
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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);
}
});
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Capabilities
LAB
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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
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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"]
}
}]
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Capabilities
LAB
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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
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Capabilities
LAB
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Paint PWA Capabilities
Progressive
Enhancement
PWA Bootcamp
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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
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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)
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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()
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Progressive Enhancement
LAB
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Q&A
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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!
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Summary
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Thank you
for your kind attention!
Christian Liebel
@christianliebel
[email protected]