Building Scalable, Maintainable Apps Using TypeScript and React
Kamran Ayub
patterns and practices
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Work at Target
What do I want?
To make my apps easier to maintain
To make my apps easier to scale
Scalable
?
Scalable
Easy to extend
Easy to collaborate on
Easy to reuse code
Maintainable
Easy to refactor
Easy to understand
Easy to test
A familiar story...
TypeScript
JavaScript that scales
- Static type checking
- Fantastic editor tooling
- Refactor-friendly code
React
Component-based presentation
- Small surface area
- Reusable components
- Functional characteristics
- Great performance
A better way is possible
ktomg.com
- Built in .NET
- Hybrid app
- Originally JavaScript & Knockout.js
- Migrated to TypeScript & React
- Heavily interactive UI
Based on a true story
(work in progress)
Concepts
- Store - Single source of truth for app
- State - The data representing the app at a point-in-time
- Actions - Object with a "type" property
- Action Creators - Small functions that create actions
- Reducers - Take actions and update Redux state
Folder Layout
State & Reducers
Actions
Props & State
Action Creators
+ bonus: Jest / CSS-in-JS
Folder layout
(previous)
- Files are spread out
- Components folder doesn't scale well
- Fine for a small site
Folder Layout
Folder layout
(new)
- Proposed by Ryan Florence
- Screen organization
- Scalable nesting
- Better collaboration
- Colocate related files
- Closer imports
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Module Resolution
Not scalable as screens nest further
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Module Resolution
Maintains F12 Go to Definition behavior
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Module Resolution
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Module Resolution
Folder Layout
There's an open issue for emulating "module directories" functionality from Webpack/Jest to allow paths like:
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- ✅ Scalable folder structure
- ✅ Avoids ../../ nesting
- ✅ Supports TypeScript and dev tools
- 😐 No module dirs support yet
Folder Layout
Redux State
"Bottom up" state
State & Reducers
No need to define an entire representative "State" interface. Just export what it will end up being (typeof)
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Redux State
"Bottom up" state
Each screen will define its state shape
State & Reducers
Folder Layout
Redux State
"Bottom up" state
State & Reducers
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Reducers
Combining reducers
State & Reducers
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Reducers
Combining reducers
State & Reducers
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Reducers
Combining reducers
State & Reducers
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Reducers
Combining reducers
State & Reducers
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Reducers
Testing reducers
State & Reducers
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State & Reducers
State & Reducers
- ✅ Maximizes type inference
- ✅ "Bottom-up" composable state
- ✅ Screens manage their own state
- ✅ Using "shared" folder, you can share state
- ✅ Using RecursivePartial<T> type helper
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Actions
Using constants and typeof
A bit wordy, but pays off at scale
Actions
Folder Layout
State & Reducers
Actions
Action type helpers
Actions
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State & Reducers
Actions (Discriminated)
Actions
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State & Reducers
Actions (Mapped)
Actions
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State & Reducers
Actions (Mapped)
Creating reducer action map helpers
Actions
Folder Layout
State & Reducers
Actions (Mapped)
Actions
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State & Reducers
Actions
Actions
- ✅ Strongly-typed actions
- ✅ Reducer action handlers are typed
- ✅ Reusable type utilities
- ✅ If actions or state change, reducers break
Folder Layout
State & Reducers
Action Creators
Action Creators
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Actions
State & Reducers
Action Creators
Dispatching actions
mapDispatchToProps makes it easier to test component in isolation
Action Creators
Folder Layout
Actions
State & Reducers
Action Creators
All type-safe with intellisense
Action Creators
Folder Layout
Actions
State & Reducers
Action Creators
Action Creators
- ✅ Action creator utility
- ✅ Dispatch is strongly-typed
- ✅ Ensure actions invoked with correct args
- ✅ Testing component is easier
- ✅ Isolates action signature changes from components
- 😐 Dispatch typing is wordy, repetitive, annoying
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Actions
State & Reducers
Props & State
(stateful, non-redux)
Props & State
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Actions
Action Creators
State & Reducers
Props & State
(stateless, non-redux)
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Actions
Props & State
Action Creators
State & Reducers
Props & State
(render prop pattern)
Can pull into type alias and share
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Actions
Props & State
Action Creators
State & Reducers
Props & State
(redux state props)
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Actions
Props & State
Action Creators
State & Reducers
Need a way to get "dispatch" and separate Redux state props vs. "own" props
Extract stateless type alias to encapsulate our State and reduce DispatchProp usage
Props & State
(redux state props)
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Actions
Props & State
Action Creators
State & Reducers
Same as stateless, create encapsulated Redux component type
Props & State
(redux class component)
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Actions
Props & State
Action Creators
State & Reducers
Split Redux connected component from "raw" component for easier isolated testing
Props & State
(redux class component)
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Actions
Props & State
Action Creators
State & Reducers
Props & State
Redux type utilities
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Actions
Props & State
Action Creators
State & Reducers
Props & State
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Actions
Props & State
- ✅ Splitting OwnProps vs. StateProps
- ✅ Reduce excessive type intersections
- ✅ Reusable type utilities
- ✅ Render prop pattern typing
- ✅ Easier testing of Redux
Action Creators
State & Reducers
BONUS SLIDE
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Actions
BONUS
Action Creators
State & Reducers
Using emotion CSS-in-JS
Doesn't really have any "weirdness" with TypeScript
For Jest testing and Enzyme, reference the code for deeper examples of async testing / Redux testing