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What’s wrong with Single-Page Apps (and what to do about it) Stefan Tilkov
 stefan.tilkov@innoq.com
 @stilkov JavaScript Days 2019, Berlin "Science Museum, ceiling" by Elecé is licensed under CC BY 2.0

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@stilkov Annoying your app users in 10 easy steps

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@stilkov 1.
 Forbid the use of the back and forward buttons

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@stilkov 2.
 Send them to the home page when they hit “refresh” …

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@stilkov 3.
 … or at least ensure the browser pops up a warning window

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@stilkov 4.
 Make sure they can’t open a second browser window

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@stilkov 5.
 Let them see UI decoration and ads first, content last

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@stilkov 6.
 Make sure they can’t bookmark or send a link

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@stilkov 7.
 Don’t let Google index anything

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@stilkov 8.
 Show users a picture of your app – it’s surely better than nothing

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@stilkov 9.
 Disable assistive technologies. Who needs a screen reader, anyway?

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@stilkov 10.
 Ensure non-functioning JavaScript gives them a blank page

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@stilkov History repeating … CORBA Web WS-* REST

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@stilkov What’s the client side analogy?

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@stilkov 1) in the SOAP/WSDL sense “Web app”2) 2) built as a careless SPA “Web service”1) > Uses HTTP as transport > Ignores HTTP verbs > Ignores URIs > Exposes single “endpoint” > Fails to embrace the Web > Uses browser as runtime > Ignores forward, back, refresh > Does not support linking > Exposes monolithic “app” > Fails to embrace the browser

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@stilkov The web-native way of distributing logic Process Flow Presentation Domain Logic Data Server Client > Rendering, layout, styling
 on an unknown client > Logic & state machine on server > Client user-agent extensible via
 code on demand

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@stilkov HTML & Hypermedia • In REST, servers expose a hypermedia format • Option 1: Just invent your own JSON-based, incomplete clone • Option 2: Just use HTML • Clients need to be RESTful, too • Option 1: Invent your own, JS-based, buggy, incomplete implementation • Option 2: Use the browser

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@stilkov A great REST hypermedia API is very similar to a simple, server-sided rendered web application

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@stilkov What does SPA even mean?

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@stilkov State Business Logic Routing Rendering Logic Look & Presentation Logic Server Client HTML

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@stilkov State Business Logic Routing Rendering Logic Look & Presentation Logic Server Client JSON

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@stilkov State Business Logic Routing Rendering Logic Look & Presentation Logic Server Client JSON JSON API JSON Client

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@stilkov State Business Logic Routing Rendering Logic Look & Presentation Logic Server Client JSON JSON API JSON Client

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@stilkov Single Page Apps – Why Routing? Solution:
 Store some app
 state in the URI! Bookmarks? Deep links? Reload?

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@stilkov State Business Logic Routing Rendering Logic Look & Presentation Logic Server Client JSON JSON API JSON Client

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@stilkov State Business Logic Routing Rendering Logic Look & Presentation Logic Server Client JSON JSON API JSON Client (Pre-)Rendering Logic Routing HTML

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@stilkov Prerendering

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@stilkov Hydration How to simulate readiness? What about Events (Clicks etc)? How to match server-side HTML to client-side DOM?

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@stilkov State Business Logic Routing Rendering Logic Look & Presentation Logic Server Client JSON JSON API JSON Client (Pre-)Rendering Logic Routing HTML

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@stilkov Special case: Searchability No Hydration needed

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@stilkov State Business Logic Routing Rendering Logic Look & Presentation Logic Server Client JSON JSON API JSON Client (Pre-)Rendering Logic Routing HTML Hydration

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@stilkov State Routing Rendering Logic Look & Presentation Logic Server Client JSON JSON Client (Pre-)Rendering Logic Routing HTML Hydration Business Logic JSON API State Business Logic Same functionality,
 different languages!

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@stilkov State Routing Rendering Logic Look & Presentation Logic Server Client JSON JSON Client (Pre-)Rendering Logic Routing HTML Hydration Business Logic JSON API State Business Logic Much, much more JavaScript

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@stilkov

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@stilkov Everyone has JavaScript, right? All your users are non-JS while they're downloading your JS If they're on a train and their net connection goes away before your JavaScript loads, then there's no JavaScript. Did the HTTP request for the JavaScript complete? Does the corporate firewall block JavaScript? Does their ISP or mobile operator interfere with downloaded JavaScript? Does their browser support the JavaScript you’ve written? Do your users get the JavaScript?

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@stilkov The cost of JavaScript in 2019

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@stilkov What’s the alternative?

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@stilkov ROCA: Resource-oriented Client Architecture http://roca-style.org

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@stilkov ROCA RESTful Server-side HTML (SSR) Application logic only on server No duplicated logic on client + No application logic on client! Client-side (self contained) JavaScript components =

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@stilkov Client Side Logic is generic Presentation logic only. It enhances HTML HTML CSS Content Layout JavaScript Presentation logic

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@stilkov Progressive Enhancement A web page needs to work without graphical elements, CSS and JS This ensures our page will even work under unfavorable circumstances We also lay the foundation for accessibility Does not mean that everything needs to work without CSS and JavaScript It means that the fundamental functionality of our web page relies on HTML only Every thing that goes beyond that is seen as an enhancement

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@stilkov $('.multiselect', context).each(function() {
 $(this).multiselect({
 selectedList: 2,
 checkAllText: "Alle",
 uncheckAllText: "Keinen"
 }).multiselectfilter({label:"",
 width:"200px"});
 });

 Project
 
 DISCOVER
 IMPROVE
 MAGENTA
 ROCA
 ROCKET
 


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@stilkov http://rocair.herokuapp.com http://roca-airways.herokuapp.com

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@stilkov Components

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@stilkov Browser Platform Component Application JavaScript Framework Component Component Component

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@stilkov Browser Platform Application JavaScript Framework Component Component

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@stilkov Browser Platform Component Component Component Component Application Component

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@stilkov Component 
 
 Browser Platform Component Component Component Application

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@stilkov Component Browser Platform Component Component Component Glue Code Application

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@stilkov $("input.date").datepicker();

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@stilkov
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@stilkov
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@stilkov
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$(".tabs").tabs(); Unobtrusive JavaScript

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@stilkov Component Browser Platform Component Component Component Glue Code HTML JS CSS HTML JS CSS HTML JS CSS HTML JS CSS ✓ Progressive Enhancement

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@stilkov Component Browser Platform Component Component Component Glue Code HTML JS CSS HTML JS CSS HTML JS CSS HTML JS CSS ✓ Progressive Enhancement Progressive enhancement is not about dealing with old browsers, it's about dealing with new browsers. — Jeremy Keith (@adactio)

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@stilkov
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@stilkov
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$(".tabs").tabs();

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@stilkov
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$(".tabs").tabs();

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@stilkov
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$(".tabs").tabs(); Custom Elements

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@stilkov Component Browser Platform Component Component Component Glue Code

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Why the hate? @stilkov

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@stilkov General benefits

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@stilkov Classic, server-side rendered web applications are much simpler, use less bandwidth, scale better, are more resilient, and a good match for most user needs

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@stilkov Many single-page apps are built carelessly and improve developer experience (if at all) at the cost of decreased usability and architectural complexity

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@stilkov Large-scale benefits

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@stilkov Any sufficiently complicated JavaScript client application contains an ad hoc, informally- specified, bug-ridden, slow implementation of half a browser. (Me, with apologies to Phillip Greenspun) Why choose a monolith if you don’t have to?

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@stilkov In-page Cross-page JavaScript method calls Links & redirects Shared abstractions & frameworks Micro-architecture Common language runtime HTTP HTML 5 JS platform Standard Browser

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@stilkov Sometimes, JS-centric applications/SPAs are the right choice, but very rarely for every part of your system

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@stilkov If you’re a fan of single page apps,
 at least build more than one • Don’t reinvent browser integration features • Accept some inefficiency • Trade-off for framework independence • Avoid modularity à la Java EE, OSGi etc.

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@stilkov Use your favorite SPA framework – when it’s appropriate. Stick to basic, simpler stuff, when it’s sufficient – likely, most of the time.

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@stilkov Stefan Tilkov @stilkov
 stefan.tilkov@innoq.com
 Phone: +49 170 471 2625 innoQ Deutschland GmbH Krischerstr. 100 40789 Monheim am Rhein Germany Phone: +49 2173 3366-0 innoQ Schweiz GmbH Gewerbestr. 11 CH-6330 Cham Switzerland Phone: +41 41 743 0116 www.innoq.com Ohlauer Straße 43 10999 Berlin Germany Phone: +49 2173 3366-0 Ludwigstr. 180E 63067 Offenbach Germany Phone: +49 2173 3366-0 Kreuzstraße 16
 80331 München Germany Phone: +49 2173 3366-0 @stilkov That’s all I have.
 Thanks for listening!

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@stilkov www.innoq.com OFFICES Monheim Berlin Offenbach Munich Hamburg Zurich FACTS ~150 employees Privately owned Vendor-independent SERVICES Strategy & technology consulting Digital business models Software architecture & development Digital platforms & infrastructures Knowledge transfer, coaching & trainings CLIENTS Finance Telecommunications Logistics E-commerce Fortune 500 SMBs Startups