Building front-end apps that Scale - FOSDEM 2014

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Developing large apps is difficult. Ensuring that the code is consistent, well structured, tested, and that the architecture encourages maintainability is essential. When it comes to building large server-focused apps the solutions to this problem have been tried and tested. But, how do we achieve this when it comes to HTML5 single page apps?

BladeRunnerJS is an open source developer toolkit and lightweight front-end framework that has helped the company I work for (Caplin Systems) ensure that a 200k LoC JavaScript codebase hasn’t become a tangled mess of unstable spaghetti code (with bacon bits). This codebase is then delivered to customers, along with around 50k LoC example functionality for them to build upon, and they're expected not to turn that into a tangled ... you get the idea.

In this talk you'll learn about the main concepts we have applied, how we have applied them - and how you can too - to achieve what might sound like the impossible.

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Building front-end apps that Scale - FOSDEM 2014

  1. 1. Building front-end apps that Scale
  2. 2. Phil @leggetter phil@leggetter.co.uk Caplin Systems ! ! ! @BladeRunnerJS
  3. 3. Overview • What is a Large Scale front-end App? • What are the signs of scaling? • What are the solutions? (with demos)
  4. 4. What is a large-scale JavaScript app?
  5. 5. 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. –Addy Osmani, Patterns For Large-Scale JavaScript Application Architecture
  6. 6. Great. More detail please!
  7. 7. Large Codebase More functionality = More code
  8. 8. Caplin Trader • SDK: • Getting Started App: • ~1,000 JavaScript files • ~425 JavaScript files • ~131,000 LoC • ~50,000 LoC ~131 lines per file • ~117 lines per file ~650 test files • ~200 test files • ~21,000 test LoC • • • ~95,000 test LoC
  9. 9. Complexity
  10. 10. Gmail & Caplin Trader • Large Single Page Apps (SPAs) • Complex functionality • Complex interactions • • • User Technology Leave open all day
  11. 11. Contributors The Human Factor
  12. 12. Who contributes to an app? • Front-end devs • Back-end devs • Designers • QA • Infrastructure and release engineers • Technical authors
  13. 13. People who are part of... • Large teams • Multiple teams • Teams spread across an organisation • Teams spread across multiple organisations
  14. 14. 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 within an application codebase and UI 3. make sure that all contributors can work in harmony 4. development must be a productive experience 5. ensure all these compliment each other
  15. 15. Seven signs of scaling?
  16. 16. Dev Setup takes forever • Lots of infrastructure dependencies • Database • Auth service • Realtime server • One or more Web APIs • Dev app server
  17. 17. My App won’t load! • Run full application • All back-end components running • Lots of moving parts
  18. 18. My App isn’t working! • Other contributors breaking functionality • Code accessed and modified from elsewhere • Dependency Analysis and bundling out of order
  19. 19. Finding assets is hard
  20. 20. What does this code do? • Inconsistent coding style and structure • Side effects
  21. 21. Long App Reloads
  22. 22. Have the tests finished yet? • Having to run all the tests • UI-based tests • Continuous Integration…taking 8 hours!
  23. 23. Scaling Solutions
  24. 24. Goals • Streamlined developer workflow • Consistency • Focus on building a single feature (in isolation) • Scalable loosely-coupled application architecture • Quality at its core (maintainability)
  25. 25. Developer Workflow
  26. 26. Building a single feature in isolation
  27. 27. Blades
  28. 28. Blade Demo
  29. 29. Application Architecture
  30. 30. Requires an Architecture that… • Allows complex interactions • Allows components to be changed without side effects • At launch and during runtime • Is easily extended • Is easily tested • Is easily maintained
  31. 31. Blades (again)
  32. 32. MVVM
  33. 33. Services
  34. 34. What is a service? • Use services to access resources • • Restful Service • • Persistence Service Realtime Service Perform common non-UI tasks e.g. • • LoggingService Services registered and accessed via a ServiceRegistry • Dynamic Service Locator 1 1 http://martinfowler.com/articles/injection.html#ADynamicServiceLocator
  35. 35. Why use services? • Used for cross-cutting concern • Functionality encapsulated behind an interface • Loose-coupled communication • Dependencies can be injected at: • App/Workbench load time • During runtime
  36. 36. Services Demo
  37. 37. Quality
  38. 38. Manually test in the workbench as part of iterative development cycle
  39. 39. Simple Wins • Consistency • • • Architecture Coding style and structure Loose coupling (MVVM, Services and beyond) • • • Facilitates testing Can easily swap out implementations Avoid testing the DOM
  40. 40. Biggest Win • Testing features in isolation • • • Change view model and assert against mocked Service Inject mock service, make calls and assert View Model Run small suit of Application End-to-End Business Tests
  41. 41. Need Proof? Our full suite Caplin Trader testing time went from 8 Hours to 10 minutes
  42. 42. A note on deployment • The BladeRunnerJS app replicates previous sole target production environment: J2EE • You can enable dev mode (discussions ongoing) • You can build to a .WAR frill • Flat File deployment coming soon (very soon, I hope)
  43. 43. Summary • Streamline developer workflow for productivity • Build features in isolation (grouping assets together) • Services e.g. EventHub for loose coupled communication • Encapsulate using Interfaces • Test a feature ViewModel < - > Service. Avoid the DOM. • It all improves Quality and thus maintenance
  44. 44. Phil @leggetter phil@leggetter.co.uk Caplin Systems ! ! ! @BladeRunnerJS bladerunnerjs.org

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