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Developing large apps is difficult. Ensuring that code is consistent, well structured, tested, maintainable and has an architecture that encourages enhancement is essential. When it comes to large server-focused apps, solutions to this problem have been tried and tested. But, with the ongoing dramatic shift of functionality into the browser, how do you achieve this when building Front-End Web Apps? In this talk we’ll cover the signs to watch out for as your HTML5 SPA grows and provide examples of some of the tooling types that can contribute-to - as well as ease - the growing pains. Finally, we’ll demonstrate how tooling can be used to support a set of conventions, practices and principles that enable a productive developer workflow where the first line of code is feature code, features can be developed in isolation, code conflicts are avoided by grouping assets by feature and features are composed into apps. The demonstrations will use the BladeRunnerJS open source developer toolkit, but the concepts are widely applicable.
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How to Build Front-End Web Apps that Scale
2014
What is a large-scale JavaScript app?
–Addy Osmani, Patterns For Large-Scale JavaScript Application Architecture
In my view, large-scale JavaScript apps are non-trivial applications requiring significant
developer effort to maintain, where most heavy lifting of data manipulation and display falls to
the browser.
Large CodebaseMore functionality === More code
Caplin Trader• SDK:
• ~1,000 JavaScript files
• ~131,000 LoC
• ~131 lines per file
• ~650 test files
• ~95,000 test LoC
• Typical Apps:
• ~425 JavaScript files
• ~50,000 LoC
• ~117 lines per file
• ~200 test files
• ~21,000 test LoC
Complexity
Gmail & Caplin Trader• Large Single Page Apps (SPAs)
• Complex functionality
• Complex interactions
• User
• Technology
• Leave open all day
Features: Change, Come & Go
Feature Progression
ContributorsThe Human Factor
Who contributes to an app?• Front-end devs
• Back-end devs
• Designers
• QA
• Infrastructure and release engineers
• Technical authors
So, how do you ensure an application is maintainable?
1. structure a massive codebase (js, css, html, i18n, images, config etc.)
2. an architecture for complex functionality and interaction (UI and other components)
3. make sure that all contributors can work in harmony
4. promote quality
5. development must be a productive experience
6. ensure all these compliment each other
The Solutions
1. Components/Widgets/Modules
2. A Services Layer
3. MV*
4. Efficient Testing
5. Tools to Support Workflow
Prove it!
Component/Module/Feature/Blade
Finding assets is hard
/assets /feature-name
Long App Reloads
Image of app partially workingWho Broken the
App?
Running in isolation ===
Faster reload times
Compose Components/Modules
into Apps
Services
What is a service?• Use services to access shared resources
• In-app inter-component messaging
• Persistence Service
• RESTful Service
• Realtime Service
• Services are a Contract/Protocol/Interface
Using Services• Use a unique identifier for each service
• Register (code or config). Code example:
!
• Get
http://martinfowler.com/articles/injection.html#ADynamicServiceLocator
Why use services?
• Features should not directly communicate
• Easily change implementation
• Implementations can be injected for different scenarios:
• Workbench / Test / App
Fake Services
Fake/Stub/Mock Services
Real Services
Efficient Testing (We’ll get to MV*)
Don’t Touch that DOM
MVVM
End-to-End Module Testing
• Testing features in isolation
• Change view model and assert against mocked Service
• Inject fake service, make calls and assert View Model
Need Proof?Our full suite Caplin Trader
testing time went from
>8 Hours
< 30 minutes
Much less for a single feature
Tooling & Developer Workflow Focus on Features
What tooling offers?
Automation
• Define workflow & promote consistency
• Scaffolding
• Dev Server
• Builds/Bundling
• Tests
Intelligence
Compliance
Dependency Analysis
Knowledge of Runtime Scenarios
• Workbench (dev-mode)
• Test
• App
Customization
• Augment workflow
• Identify allowable change to workflow
• Automation commands
• Builds/Bundling
• Test Runner
Proven!1. structure a massive codebase - by feature
2. an architecture for complex functionality and interaction - Services & MVVM
3. contributor harmony - separation of concerns; codebase structure, modules/components & architecture
4. promote quality - Services & MVVM === Highly testable
5. productive experience - tooling supports all of this & ensure consistency
6. complimentary - Yes, look at all the cross-over!
