Offline First (Web) Apps - Beuth-Hochschule Berlin 2016

Oﬄine-First
(WEB) APPS
Alex Feyerke / @espylaub
Jan Lehnardt / @janl
Beuth-Hochschule 2016, Berlin
Hallo!
[Einleitung]
Wir sind Teil des Teams, das Hoodie baut…

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HOOD.IE
ein open-source-server plus frontend-bibliothek, mit dem man schnell komplette web-apps mit nutzern
und daten und allem bauen kann, hauptsächlich vom browser aus. Es ist wie jQuery für daten. Und
Hoodie ist noch deswegen speziell, weil man Hoodie-Apps immer ofﬂine-fähig sind, gehen also nicht
kaputt wenn die Verbindung mal schlecht oder weg ist. Deswegen interessiert uns die ganze Sache so.
Aber der Talk handelt nicht von Hoodie, sondern von…

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Oﬄine-First
Concepts
Interfaces
Experiences
Problems
Ofﬂine First.
Und zwar nicht besonders technisch, alles. Es geht um
Konzepte, Interfaces, Experiences, und allgemeines Verständnis des Problems.
Bevor wir anfangen, machen wir einen kleinen umweg, und sprechen mal allgemeiner über das Bauen.

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Von 1933 to 1957 gab es das Black Mountain College in North Carolina.
Denker, Künstler, Wissenschaftler aus aller Welt kamen zusammen, um Bildung neu zu denken,
ganzheitlich zu machen, Kunst, Wissenschaft und Handwerk als Einheit zu verstehen. Einer der
Lehrenden war…

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Bucky
Buckminster Fuller. Der Typ mit den geodätischen Kuppeln. Hier mit Kuppel. Er dachte, Kuppeln wären
die Zukunft der Architektur.

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Bucky
Also hat er für die Weltausstellung 1967 in Montreal eine gebaut. Die Zukunft war im Anmarsch, und das
Bauen sollte das widerspiegeln: neue Formen des Zusammenlebens, neue materialen, neue formen.
Und Kuppeln hatten viele Vorteile: höhere Stabilität, weniger Rohstoffe, efﬁzienter zu heizen… klang
unwiederstehlich. Efﬁzient, robust, hoch ästhetisch und geometrisch perfekt.
Also warum leben wir nicht alle in Kuppeln?

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In der hier lebt schonmal niemand, die ist abgebrannt. Aber so allgemein: wir sind doch jetzt in der
Zukunft! Wo sind die Kuppeln?
Stellt sich raus: Menschen wollen Behausungen, die sie sich zu eigen machen können, die simpel,
anpassungsfähig und ﬂexibel sind. Ziegel, Holz, Beton, rechte Winkel: einfach, verlässlich,
vertrauenswürdig. Total traditionell. Kling langweilig konservativ, macht aber auch sinn. Man möchte
etwas, was sich am echten leben orientiert, und wo man auch mal ein regal in die wand schrauben oder
sich aus dem fenster lehnen kann. Muss nicht perfekt sein. Wir sind ja auch nicht perfekt. Und als das
Black Mountain College anbauen mussten…

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haben sie eine Kiste hingestellt.
Paradoxerweise ist die konservative option in solchen fällen oft auch die anpassungsfähigste, die mit
dem echten leben am kompatibelsten ist.

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Behaltet das alles mal im Sinn, wenn wir jetzt wieder in die Gegenwart düsen und schauen, wie wir so
Sachen bauen.

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Wie wir arbeiten
MEHR ODER WENIGER
SCIENCE FICTION
We make web apps. Or native apps, for our purposes, it doesn't make a difference. But we make, and
while we make, we imagine those things we make in their completed, working, usable state. We imagine
them in the future, where all the cool people are using our stuff and making us rich and famous.
But we‘re always saying: „In the near future, when this is ready, your life will improve a tiny bit“
And too often, our industry will communicate this like glossy science ﬁction:

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Small companies like plastc, this „20 credit cards in one“-hardware startup, and like most pre-order/
crowdfunding companies, they have a vision, and they have a video. And it‘s basically a tiny slice of
science ﬁction, a year or two from now: „here‘s how we imagine real human beings behaving in the near
future“.
And of course they show the tech and all, but it doesn‘t really matter what the product is, they all work by
showing this evocative shiny, perfect and slick future.
[plastc.com]

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And this scales throughout the industry. Microsoft, also loves imagining the future. They regularly
release a so-called "Productivity Future Vision". Now, the name sounds as if someone just pulled three
human resources buzzwords from a hat, but let‘s take a look at the current one:

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https://www.youtube.com/watch?v=w-tFdreZB94
Microsoft‘s Productivity Future Vision 2015
But it feels… wrong. It's too smooth. It's not normal enough.
But it‘s the future! Every ﬂat surface is a screen! You‘re always connected, under water, in rural
Cambodia, everywhere. The network is perfect, so your devices have no signal indicators. Your batteries
are perfect, so your devices have no battery indicators either.
Source: https://www.youtube.com/watch?v=w-tFdreZB94

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Everyone's happy, nothing is broken or
smudged. There is infinite wi-fi with
infinite bandwidth, no batteries run out,
no traffic, no delays.
—Tobias Revell
Critical Design / Design Fiction
All the systems in these videos are always flawless.
„Everyone‘s happy…“, even old grandad with his wonky knee, because the humans may fail, but the
systems always work.
And by the way, you should absolutely look up Tobias Revells‘s work, it's eye-opening and very well
done, which is why I'm stealing a bit more of it.
Now, Google Glass used to be the future, now it‘s the past, but while it was still a thing, of course Google
made a near-future sci fi video for it:
[source: http://blog.tobiasrevell.com/2013/12/critical-design-design-fiction-lecture.html]

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https://www.youtube.com/watch?v=v1uyQZNg2vE
Google Glass Promo Video
This is marginally better: there‘s normal stuff like playing with dogs or a being late for a ﬂight, but the
basic symptoms are the same: the people, the lives, the circumstances: most of them are outliers, all
very privileged people in a kind of post-scarcity scenario where, as Revell puts it, "it's a classic case of
everyone suddenly being an ice sculptor and ﬂying around in balloons". It's also not normal. And again:
the systems are perfect where the humans aren‘t.
It again assumes a perfect, global network, even in the sky, so it‘s still improbable, but has hints of
normality.
And now:

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Kurz zurückspulen
This next one is from 1969, with a vision of the 1990s. Same era as the Montral Dome from a minute
ago. So I‘d just like you to picture that in your mind for a second. The future, seen from the 60‘s. You‘ve
all seen the movies. Ok?
Now consider that this was made by the British Post Ofﬁce…

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https://www.youtube.com/watch?v=ONESDY9KMes
Post Office in the 1960s - A glance 30 years into the future
from Dollis Hill Research Station
It seems rather normal. Why is that? Because it‘s not perfect. We see normal people at normal desks in
an normal office. Also: the very first thing that happens: it doesn't work properly. The guy at the other end
can‘t understand anything. And the weather's bad. Because it's London. It‘s normal. Listen: "suppose
she makes an error". People don‘t make mistakes in Microsoft‘s future vision. Nobody has to ask glass
to do something twice in the google thing.
And the topics? Leases, bank statements, mortgages… normal normal normal. It's mundane, it's a bit
wonky, but it's everyday life.
What this shows is that thinking about the future is obviously a bit hard, because…

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[…] for every miraculous iPad there are
countless partly broken realities: WiFi
passwords, connectivity, battery life,
privacy and compatibility amongst
others.

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The real skill of creating a compelling
and engaging view of the future lies not
in designing the gloss, but in seeing
beyond the gloss to the truths behind it.
—Nick Foster
The Future Mundane
Source: http://www.core77.com/blog/columns/the_future_mundane_25678.asp

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And I just said this when speaking about this product sci-ﬁ:
„here‘s how we imagine real human beings behaving in the near future“
But what I really mean, and what you really want, is
„here‘s how we imagine something utterly normal happening in the near future“

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Wir sind
nicht normal
I'm showing you all this because we, as, and I'm sad to have to say this from up here, as well-educated,
well paid people in the tech industry in a super-wealthy country, we're also not normal.

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And the circumstances in which we work aren't normal either, they usually bear little relationship to how
and where our products will probably be used. We build from behind shiny new macs with full-sized
keyboards in well-equipped ofﬁces with fast connections, but the target environments are radically
diverse and different.
And that‘s just us in our normal ofﬁces. The closer you get to San Francisco, the exponentially less
normal things get.

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Thing is: It used to be that if your device could consume the web, it could also make it. That‘s no longer
true for the majority of people.
So you had to learn that people‘s devices were different than your dev machine, and now you realize
that their circumstances are also very different, and require a bit of an empathic leap.
Because their experience of the web is not only different to ours, it‘s also different to our historical
experience of the web. Their ﬁrst contact is radically different than ours was.
But what counts for us, now, is that:

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Unser Umstände
deﬁnieren unsere
Denkweise
We have the best tools and the best infrastructure available to us, and of course, that informs our
mindset when we build all the new shiny future things.

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BART 2
An extreme example: If you take a google/apple/ebay/facebook bus to work, you don't get the usual
public transport experience. You've got free corporate wiﬁ, air conditioning, leather seats… your
commuting experience is far, far removed from that of basically everyone else. That‘s probably your
baseline now.
But in a way, we‘re all on the google bus. We‘re super privileged. And we frequently forget that we have
to…
[http://www.wired.com/2013/09/mapping-silicon-valleys-corporate-shuttle-problem/]

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Baut für
eine normale Welt
Normality is where most of life happens.

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Baut für
eine mobile Welt
And the normal world, with all the normal people it, that have average budgets and average resources,
that world, from your perspective as a developer, is overwhelmingly mobile. Phones are mobile, tablets
are mobile, this thing is mobile. This is a mobile device. Hundreds of thousands of people use these with
3G or LTE sticks. You might not, but they do.
The big grey box is a relic. Mobile is normal.

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Normalität
ist nicht perfekt
And you all know this: it's imperfect. Normality is imperfect. The web is very, very imperfect. The
experience you're building? It's going to break for people. It's imperfect in ways you can't inﬂuence. You
can write all the tests you want, but you can‘t ﬁx 3G on the subway.
And we do make attempts to import this reality into our work environments:

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I saw a talk the other day that showed this image, stating that „this is the internet now“.
But that‘s not true. That‘s superﬁcially what it looks like, on the surface, but what that is is a bunch of
devices connected to a local dev server that‘s propably in the same room. But that iPad‘s never going on
a plane, and that kindle will never be on the subway, and that game boy… doesn‘t matter.
The point is not that you have to carry all those devices around in the world for testing, but rather that…

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…you can now build experiences to accommodate this normality, experiences that go beyond your apps
just breaking, becoming unresponsive, showing empty views, losing data, making people nervous with
panicky error messages. You can now build your apps in ways that acknowledge the fact that the web is
imperfect, that your connections to it are also imperfect, and you can provide good experiences
regardless.

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Oﬄine ist
kein Fehler
because Ofﬂine is not an error.

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Oﬄine ist
im mobilen Leben
einfach Alltag
and therefore…

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Oﬄine ist
im normalen Leben
einfach Alltag
It‘s just a state your app can be in. And a fairly likely one at that. It‘s not exactly an edge case.
So here‘s the basic idea behind Ofﬂine First:

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Treat the network as
an enhancement
OFFLINE-FIRST
IN EINEM SATZ
Wie in progressive enhancement. Beyond the ﬁrst load, just don‘t assume you have a network
connection.
So how does that work, conceptually? Let‘s take a quick look at Hoodie‘s

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Offline-First-
Architektur
AM BEISPIEL VON HOODIE
offline-first architecture. Just to see one way to do his whole thing.

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WAS MUSS OFFLINE SEIN?
An App's ofﬂine capability is guaranteed through two separate aspects:

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• Die App + assets
- the app itself and its assets must be available ofﬂine. This is done through Appcache or Serviceworker,
or through a native wrapper such as phonegap or electron. In a native app, this is a given.

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• Die App + assets
• Die Daten der App
more interestingly, the app must handle data in a way that doesn't require a connection. This is best
done by reading and writing through a local data store which syncs, when possible, to the server.
Let‘s see how hoodie handles this.

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FRONTEND BACKEND
Hoodie Sync

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FRONTEND
App
BACKEND
Hoodie Sync

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FRONTEND
App
hoodie.store
BACKEND
Hoodie Sync
The app only ever talks to the hoodie API, never directly to the server-side code, the database, or even
in-browser storage.

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FRONTEND
App
hoodie.store
browser store
BACKEND
Hoodie Sync
[explain slide]
As far as this concept goes, feel free to replace localstorage with any in-browser storage of your choice.
This, by itself, is enough for an app. You can wrap that in node-webkit and sell it to people who don‘t
trust the cloud. But let‘s assume you want more, you want user management and syncing.

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FRONTEND
App
hoodie.store
Sync
CouchDB
REST
BACKEND
Hoodie Sync
browser store
[explain slide]
We can do syncing because each user has their own little private database which only they can access.
So it‘s very simple to decide what gets synced. It‘s the user‘s private data. Of course it should be on their
machine, and we can easily keep people‘s data separate on the server.

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FRONTEND
App
hoodie.store
Sync
Plugins
(node.js)
CouchDB
REST
BACKEND
Hoodie Sync
browser store
So, how does it work?
[Explain a direct message moving through the system]
So we never have element talk directly to each other. They only leave each other messages and tasks,
like passive aggressive roommates. It‘s all very loosely coupled and event-based. Which means that it
can be interrupted at any stage without breaking. Messages and tasks will be delivered and acted upon
whenever possible. It‘s designed for eventual consistency.

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FRONTEND
App
hoodie.store
BACKEND
Hoodie Sync
Sync
Anyone home?
Out for lunch,
BRB
browser store
The nice thing is: in most cases, the frontend doesn‘t care whether the backend is actually there or not.
It will hang on to your data and sync whenever it can, and if your UI allows it, users can keep working
without interruption.

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FRONTEND
App
hoodie.store
BACKEND
Hoodie Sync
Sync
I don‘t care!
Out for lunch,
BRB
browser store
offline first apps are the web's honey badgers: they don't care, they just do their thing. Bees, tunnels,
bad connectivity: the offline badger just keeps on going. It's how things should be on the internet: robust
and fault-tolerant.
Anyway, the point was:

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FRONTEND
App
hoodie.store
Sync
Plugins
(node.js)
CouchDB
REST
BACKEND
Hoodie Sync
browser store
If you want true ofﬂine capability, your app shouldn‘t try to talk to the server directly, only through sync.
And you always want to keep a local copy in browser storage. That‘s really the central point: the user‘s
data on the user‘s device, always.
Sync is pretty hard. Really. You probably don‘t want to be implementing this yourself, there‘s just so
much to get wrong.
But whatever tech you choose to solve this with:

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Getting into the offline mindset requires only
one key realisation: when you leave the world
of timely, reliable communication, the local
database, not the server’s, must be the
gateway for all persistent changes in
application state.
— Aanand Prasad
Offline Support is Valuable, and You Can’t Add it Later
So then, the big question:
[http://aanandprasad.com/articles/offline/]

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Ok, wie funktioniert
diese Oﬄine-
Zauberei?
Magiiiiiiic spaaarkles

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// Store some data
hoodie.store.add('todo', {name: 'Go to Wedding'})
Hoodie-Beispiel
No magic, just a line of code.
This is what using hoodie looks like. There‘s a hoodie object, with a store object, which has a couple of
methods, like „add“. Add expects a type (todo) and an object with data in it.

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// Store some data
// Sign up a new user
hoodie.account.signUp('[email protected]', 'secret');
Hoodie-Beispiel
Sign up a new user: use the API

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// Store some data
// Listen for store events
hoodie.store.on('add', handleNewObject)
Hoodie-Beispiel
Want to know when something changed so you can update the UI?
Listen to events from the library

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// Store some data
Hoodie-Beispiel
Und wie mach ich das jetzt oﬄine?
So how do you make this work ofﬁne?

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// Store some data
hoodie.store.add('todo', {name: 'talk to students'})
Hoodie-Beispiel
Gar nicht. Das war’s schon.
All you need to do is embrace a decoupled, event based architecture, which you probably do anyway.
Talk to the api, let it sync for you, and listen to events from Hoodie to see if anything happened.
And that‘s it. It‘s not a special feature you have to explicitly invoke, it‘s how the entire architecture works.
You get ofﬂine for free.
Let‘s just see that in action:

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We trust the CouchDB for the server. It‘s a database that replicates, which is exactly what we want for
syncing.

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{
"key": "value",
"number": 1,
"numbers": [2, 3, 4, 5],
"sub-thingie": {
"yes?": true
"no!": false
}
}
JSON-Dokumente in CouchDB

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{
"_id": "value",
"_rev": "1-F00B44476123…",
"numbers": [2, 3, 4, 5],
"sub-thingie": {
"yes?": true
"no!": false
}
}

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{
"name": "Alan Turing",
"birthday": [1912, 07, 23],
"hero": true,
"notable-awards": {
"OBE": 1945,
"Royal Society": null
}
}

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{
“_id": “alan_turing",
"name": "Alan Turing",
...
"_attachments": {
"portrait.jpg": {
"content-type": "text/jpg",
"size": 30675
}

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A B
2 databases that
sync with each other

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A B
DOC A [4-D,3-C,2-B,1-A]
DOC A [3-C,2-B,1-A]
DOC A [2-B,1-A]
DOC A [1-A]
DOC A [3-C,2-B,1-A]
DOC A [4-K,3-C,2-B,1-A]

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DOC A [5-L,4-K,4-D,3-C,2-B,1-A]
A B
DOC A [4-D,3-C,2-B,1-A]
DOC A [3-C,2-B,1-A]
DOC A [2-B,1-A]
DOC A [1-A]
DOC A [3-C,2-B,1-A]
DOC A [4-K,3-C,2-B,1-A]
DOC A [[4-K,3-C,2-B,1-A],[4-D,3-C,2-B,1-A]]
DOC A [[4-K,4-D],3-C,2-B,1-A]
DOC A [4-K,4-D,3-C,2-B,1-A]

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Knaller.
Wie geht’s weiter?
So, we felt like we'd solved a lot of the technical aspects, and now we were wondering: what does this
mean? Which opportunities does this give us, exactly? Which problems can we now solve?
And in my research I noticed I was suddenly reading articles from an area of computer sciences I really
wasn‘t expecting. Because if you have several data stores with the same data in your system…

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In der mobilen Welt
bauen wir alle
verteilte Systeme
… you‘ve got a distributed system, for better or worse. And now a whole new range of interesting
problems and opportunities arise. But before we even go there, we can look at some insights from the
distributed systems world and see whether they can help us.
And as we all know, there are only two hard problems in distributed systems:

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Seriously though.
There are three things that pop up again and again:

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— Tyler Treat
Distributed Systems are a UX Problem
1. The cost of knowing the „truth“ is
prohibitively expensive
A vendor is selling you a thing, but the vendor's system is not actually checking whether the item is
actually present in the warehouse, or even if the warehouse still exists. It might be on ﬁre, for all the web
interface knows. But doing this check is prohibitively expensive and also quite challenging. There are
other factors. Five other people may simultaneously buy something that is only in stock once. You could
throw lots of money at engineering and try and make this perfect, and prevent four of those sales. But
you're really pushing the limits of practicality. It is much more sensible to have your systems make
educated guesses and assumptions, and make trade-offs on the few occasions when they're wrong. And
then apologise to people, and recover from these edge cases and race conditions.

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— Tyler Treat
2. There is no „now“
This is just physics. The parts of your system are not just distributed conceptually, there are actual
physical distances between them, and there is latency between them. Your data realities can partition
and end up on separate timelines that you have to merge again.
And that means that…

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— Tyler Treat
3. Failure is not only an option, it‘s an
inevitability
Warehouses catch ﬁre. Connections go down. Networks partition. Hardware fails. The software is buggy.
We can‘t know everything, we can‘t control everything. So how can we gain certainty about anything?

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— Tyler Treat
3. Failure is not only an option, it‘s an
inevitability
Now Tyler here is urging us to stop trying to build perfect systems, but this is only half of our problem:
You're building your app to be perfect, but at the same time, you're expecting the systems it runs on to
be perfect, too. Just like in the Microsoft and Google videos assume a perfect world for their apps and
services to run on.
Anway, these three points aligned nicely with the problems people were having with ofﬂine scenarios:

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Because we held workshops and talks, wrote blog posts and spoke to lots of people about this. We were
surprised at how many developers suddenly opened up about their offline troubles—realizing they’d had
similar problems in the past, but never spoken to others about them, because it wasn‘t a thing.
People had veeeery interesting and specific problems, ranging from building, and I quote, „runkeeper for
fish“, for anglers in the norwegian wilderness, to several people trying to build super robust point-of-sale
systems for places with bad connectivity.
But we identified some central themes:

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Vertrauen und
Verlässlichkeit
OFFLINE-PROBLEME
The ﬁrst and most pressing issue people seem to have is that they can‘t trust their apps to do the right
thing when the connection gets dodgy. You can summarize this with the following user story:

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Ich möchte, dass ich auf
meine Daten tatsächlich
zugreifen kann, wenn ich sie
dringend brauche.
USER STORY
And this is quite fundamental. It‘s so fundamental it probably gets forgotten most of the time. Of course
users want this. But it used to be a painful problem, and it was easier to just fail, show errors and let
people blame it on the telekom.
But you can often do a lot better, and offline first is the way to go. But first, let me illustrate the problem:

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So here‘s the german railway advertising that you can apparently book tickets and use their app under
any circumstances, even when free soloing in the alps (remember, in the tech future, everyone is into
extreme sports and ice carving)

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vs.
and then there‘s the normal world with this guy who can‘t access his ticket, because the app won‘t start
up when the connection is bad. It‘ll work in airplane mode, but on an actual high-speed train, where the
connection is slow and intermittent, it fails, and it fails slowly. While the ticket inspector is breathing down
your neck. A german ticket inspector. Bad user experience.
The solution would be to store personal data and tickets locally, and not make the initial communication
with the server blocking.

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Another symptom: screenshotting apps, because you can‘t trust them to retain their state.
Who here does this?

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Lots of people do this. This is my camera roll from a recent trip to Japan. Most of my photos are
screenshots from where I was afraid that the data I‘d just fetched would vanish the next time I opened
my phone. Because this kind of thing happens a lot:

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Those views were full of data just moments before I took these screenshots, but then I made the mistake
of, I don‘t know, switching apps or putting my phone away for a minute. And what happens? The apps
ditch any data they may have had, then fail at loading new data, and then the user suddenly has no data
at all. That‘s just not cool.
So, we can use ofﬂine ﬁrst to get…

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Vertrauenswürdigere und
verlässlichere Apps
OFFLINE-FIRST CHANCEN

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Always-online-
Architektur
OFFLINE-PROBLEME
The second issue is that many apps are designed to only work while connected, even if there‘s
absolutely no intrinsic requirement to do so.
This is a relic from the age of the big grey box, of the terminal and the thin client, where all the
computing power was probably far away from you. Now it‘s in your pocket, and we can do things
differently.

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Wenn ich oﬄine bin, möchte ich
trotzdem Sachen machen
können, die nicht zwingend eine
Verbindung erfordern.
USER STORY

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If you‘re only viewing your own data, or adding data yourself, why doesn‘t this just always work, online or
ofﬂine? You should be able to add a meeting, mark a task as done, write a message, check in, post a
picture… create stuff. Store now, sync later, but don‘t get in the way of getting things done if it isn‘t
necessary. And again, this is an opportunity:

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Nützlichere
Apps
OFFLINE-FIRST CHANCE
This is directly linked to the next one:

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Meine Daten sind
nicht bei mir
OFFLINE-PROBLEME
It‘s probably on a server in the US somewhere, if you‘re lucky it‘s on a CDN on the same continent as
you.

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Ich möchte meine persönlichen
Daten immer bei mir haben.
USER STORY
It is my personal data, why should it not be on here? I might need it, and you don‘t know when. Plus, in
most syncing scenarios, I‘m the authority over my data, so just let me keep a local copy. Or rather, your
server only gets to back up my data.
Granted, this gets problematic if your app is highly collaborative, but if you have a use case where user
data is fairly well isolated, you can easily do this.
So, the potential beneﬁt is:

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Immer verfügbare
persönliche Daten
Super fast, always available and simply reliable.

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Man muss
vorausplanen, damit
eine App nützlich ist
OFFLINE-PROBLEM
One more thing that frequently irked people when we talked to them about their ofﬂine woes: apps not
being smart about what data they store locally. In short:

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Ich möchte, dass Apps ein
Wenig für mich mitdenken.
USER STORY
Because I don‘t know in advance when I‘ll be ofﬂine. If I knew, it wouldn‘t be a problem, because I could
prepare for it.

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Apps sollten idealerweise schon
die aktuellen Daten haben, bevor
man sie braucht.
Nowadays you expect your podcast app for example to download new stuff as it appears, so it‘s there
when you need it, without delay. And this is wonderful for ofﬂine, too. So think about whether your app
could hang on to data, or even pre-fetch new data for your users before they need it.
Similarly:

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Oﬀensichtlich wichtige Daten
sollten lokal verfügbar sein.
Dropbox is good in this regard. Fave something on the phone? It‘s now on the phone, always. And that‘s
a good assumption to make on their part.
You could take this further though…

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Smart, offline maps
WÄRE COOL
So sure, you can have offline maps, but you need to know that in advance. Get an offline maps app, or
get google maps to cache your surroundings.
But… maps knows where you live, right? Imagine if it would pre-emptively download your surroundings
as soon as it notices you‘re on wifi in a different city than usual.

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Smart, oﬄine maps
ABER ETWAS SPOOKY
And on the other hand, this nicely demonstrates some of the issues with caching local data: you need
new UI elements, plus you need to answer some pressing questions: how long will the cached map be
retained? Does it get ﬂushed at some point? Can I remove it when I don‘t need it anymore? Can I cache
more than one at a time, and if yes, is there some sort of limit? In short: how does it work and can I
trust it?
Or, for you as a developer: can you make it trustworthy while hiding all the complexity? Interesting
questions, but a cool opportunity:

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Apps, die Bedürfnisse
antizipieren
But that was already pretty tricky, and brings us to:

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Oﬄine-First
Herausforderungen
It‘s becoming obvious that there are a number of new things you could be doing, and that these new
things require new interfaces and in some parts even a new design language, because you have to
communicate stuff to people you haven‘t had to communicate before

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If your app behaves differently depending on whether it‘s connected or not, you‘ll probably have to make
this clear somehow.
Threema does this by displaying an always-visible connectivity stripe at the top, red for disconnected,
yellow for connecting and green for connected, and teaches you beforehand what the consequences of
each are.
Another big issue:

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save vs. sync
How do we communicate the states data can be in? Stored locally, scheduled for sync, synced, possibly
out of date, conﬂicting…
possibly out of date is a state you‘ll get quite often in ofﬂine-capable apps, and you‘ll have to decide
how crucial the age of data is, and how you communicate it. Because old data can still be useful while
potentially being wrong. Think train schedules. Could be wrong, but communicate intent. And that‘s
valuable.

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Save
But you could just as well selectively disable, hide or re-phrase features. Imagine a save button that
knows whether it‘s connected to the server, and changes accordingly:

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Save
AND SYNC LATER
Or you could just let users save either way and inform them about the state of things after the fact.
Or, you could be super-secretive…

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…and just handling everything in the background, autosaving constantly and auto-syncing whenever you
can.
And if it doesn‘t work…

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Saved locally
(oﬄine, syncing later)
…apologise and deal with it.
There are loads of ways to solve this problem, depending on the use case, who you‘re developing for,
and how crucial the data is to them.
But one thing you‘ll probably have to do is

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Nutzer über
sync-Prozesse
informieren
…inform users about sync outcomes. Not just whether they succeeded or not, but how and possibly why
data has changed in their browser. This is probably one of the hardest UI problems related to sync, for
example when it comes to chronologically sorted data, like chats or other streams/threads.

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Nutzer über
sync-Prozesse
informieren
So, I said that if users only add data, why not always just let them do that and sync later? Well, it turns
out that things aren‘t quite as simple, and that context really matters.
Here‘s a fairly simple chat example that illustrates some of the things you‘ll have to keep in mind:

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10:00 - Hi
10:01 - Yo
A
B
10:02 - Meet on Thursday?
A
10:03 - Sure, I‘m free.
B
10:04 - Ah wait, meant Tuesday.
A
Now imagine that B‘s second message was written while one of the two was ofﬂine. On a train, in a
tunnel or something.

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10:00 - Hi
10:01 - Yo
A
B
A
A
…
10:05 - Hey A
C 10:06 - Hi C
A 10:07 - Hey, you free on Tuesday?
A 10:08 - Lemme see…
C 10:09 - I asked B too, btw
A
Then the offline user reconnects and the messages sync up again. A receives B‘s missing offline
message. So where do you put it?
You can put it in the chronologically correct place, which makes sense in a thread context, because the
order carries meaning. But that might mean the message appears somewhere out of the user‘s current
view, way up there somewhere. That‘s a new UI challenge in itself. Or you could do what Imessage
sometimes seems to do: display it in the flow according to the time it arrives at.

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10:05 - Hey A
10:06 - Hi C
C
10:07 - Hey, you free on Tuesday?
A
10:08 - Lemme see…
10:09 - I asked B too, btw
A
A
A
C
You can put it in the chronologically correct place, which makes sense in a thread context, because the
order carries meaning. But that might mean the message appears somewhere out of the user‘s current
view, way up there somewhere. That‘s a new UI challenge in itself. Or you could do what Imessage
sometimes seems to do: display it in the ﬂow according to the time it arrives at.

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10:00 - Hi
10:01 - Yo
A
B
A
10:03 - Sure, I‘m free.
B
A
This guarantees that the message will actually be seen by A, but this approach has the potential to
change meaning, because message order is meaningful.
And this is only text-based, one-dimensional data. A simple chat, one of the simplest examples I could
think of.
What to do with deleted items, things that can’t be organised in lists, objects that aren’t in themselves
immutable? There‘s a lot of potential for complexity here, so that‘s something to be aware of.

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Because the web platform is becoming more an more powerful and capable. Here‘s a photo editor. It‘s
not photoshop, nor is it trying to be: it‘s quick, easy, no installation, cross-platform, auto-updates, and
does most of the things you want in a simple photo editor.
You‘d probably want it to work ofﬂine, though.

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This is an experimental collaborative multitrack recording app, with synths and drumkits and audio, and
it runs in the browser. This is part of a masters thesis by Jan Monschke, and it‘s really bleeding edge,
but just imagine where this tech will be in a year. Cross-platform garage band? That‘s pretty damn cool.
But again, it can‘t be used ofﬂine, and that‘s a disadvantage in comparison to the native apps it
competes with.
But aside from competing with native apps, what are the…

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Offline-First
Vorteile
advantages of offline first?

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• Performance
OFFLINE-FIRST VORTEILE
First: Performance. We put stuff in CDNs to move it closer to the user, but the closest thing to me right
now is this (phone in pocket).
Put your app in here.
Put your data in here.

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• Performance
NULL LATENZ
OFFLINE-FIRST ADVANTAGES
That's zero latency for me. This is the way to the snappiest experience. The data may be old, but at least
it‘s there. And in many cases, time isn‘t doesn‘t even invalidate the data, so there‘s still a beneﬁt to
having it.

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• Performance
NULL LATENZ
• Robustheit
Robustness. Ofﬂine capability protects from service interruptions. Interestingly, we hadn‘t even
anticipated this. We have a fairly large service running on Hoodie and had to brieﬂy take it down for
maintenance, and most people using the app at that very moment didn‘t notice.
Turns out: It doesn‘t matter if your app can‘t reach the server because the user is on the subway, or
because the server is down. It‘ll still work.

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• Performance
NULL LATENZ
• Robustheit
SERVER DOWN? MIR DOCH EGAL

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• Performance
NULL LATENZ
• Robustheit
• Bessere UX
Better experiences. Apps don‘t lose data. Apps are more trustworthy. Apps are more usable and useful.
Apps cause less frustration.

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• Performance
NULL LATENZ
• Robustheit
• Bessere UX
NIE MEHR SPEICHERN MÜSSEN
And remember, you‘re saving to a local store first. You can save after every single keystroke if you want,
and sync to the server every couple of seconds. Forget save buttons altogether.
There‘s a lot to be gained from an offline-first architecture that‘s not completely obvious at first glance.
Anyway:

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Die web-Plattform
ist Wahnsinn
This is just the start. Image manipulation, maturing web audio APIs, and there‘s a lot more to come. At
JSConf EU last year, there was a lot about ServiceWorker, client side storage and web crypto: all just
coming in to existence then, cutting edge, but wildly promising. And now?

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Any application that can be written in
JavaScript, will eventually be written in
JavaScript.
—Jeﬀ Atwood
„Atwood‘s Law“
And if it‘s in the browser it‘s going to be used in a mobile context, and it‘s going to be ofﬂine at some
point.
And it‘s not just about increased mobility any more:

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At some point recently, the browser
transformed from being an awesome
interactive document viewer into being
the world’s most advanced, widely-
distributed application runtime.
—Tom Dale
Progressive Enhancement is Dead
The web is very attractive platform for developers for many reasons, and as web apps gain complexity
and mobile native app usage increases further, users will simply expect a mature and solid experience.
Waiting for more cell towers to be built won‘t help them. Your apps have to work regardless of the
circumstances.
Here‘s the conclusion:
Source: http://tomdale.net/2013/09/progressive-enhancement-is-dead/

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Wir können nicht weiterhin aus unserer
Desktop-Perspektive Apps bauen, wo
langsames oder schlechtes Netz als
Problem wahrgenommen und als Fehler
kommuniziert wird.
So, in closing:
We can’t keep building apps with the desktop mindset of permanent, fast connectivity, where a
temporary disconnection or slow service
is regarded as a problem
and communicated as an error.

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The future is already here — it's just not
very evenly distributed
—William Gibson
Don‘t forget you‘re from the future, and what‘s normal to you probably isn‘t normal for the rest of the
world

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• Die Welt ist nicht perfekt
• Eure Software auch nicht
• Geht damit um
VERGESST PERFEKTION
Learn to let go a bit more. Find a sensible middle ground between certainty and assumption.

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Legt los!
Last year, I finished a prototype web app that works completely offline, it has offline maps, and it can
even take photos while offline and store them until you‘re back online. It runs well on my dodgy, nearly 4
year old android phone. It‘s only going to get easier, faster and more stable from here on out.

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Redet drüber
that this is a thing. Among developers, yes, but also among users: People need to get used to their
browsers and websites working ofﬂine.
And ﬁnally:

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Macht mit!

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We started offlinefirst.org to start bringing people together on this. We‘ve got a pretty active slack
channel and there‘s a newsletter I can really recommend. In any case, come join us!
So finally:

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be proud of that dependable boxy thing!
And also:

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Keine Panik,
Hoodie hilft
Sowohl das Projekt als auch die Leute darin.

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Danke!
@janl / @espylaub
Slides: tinyurl.com/oﬄine-ﬁrst-beuth-2016
Kommt vorbei: http://hood.ie
❤

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Offline First (Web) Apps - Beuth-Hochschule Berlin 2016

Offline First (Web) Apps - Beuth-Hochschule Berlin 2016

Alex Feyerke

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