XComponent

A microframework that combines MobX and React to solve common performance, state management, and lifecycle issues.

• Install
• Features
• Usage
  • Basic Component
  • Inline State
  • Lifecycle Hooks
  • Component Composition
• API
  • Core
  • Models
    • Value
    • AsyncValue
    • BoxedValue
    • BoolValue
• Documentation
• License

Install

pnpm add @n4s/xcomponent

Features

• Drop-in replacement for MobX observer
• Built-in state management patterns
• Simplified lifecycle hooks
• Component composition utilities
• Helper models for common use cases

Usage

Basic Component

import { X } from '@n4s/xcomponent'

const MyComponent = X<{ count: number }>(({ count }) => (
  <div>{count}</div>
))

Inline State

import { X, Value } from '@n4s/xcomponent'

const Counter = X(() => {
  const state = X.useState(() => class {
    count = new Value(0)
    get doubledCount() {
      return this.count.value * 2
    }

    increment = () => this.count.set(this.count.value + 1)
  })

  return (
    <>
      Count: {state.count.value}, Doubled Count: {state.doubledCount}
      <button onClick={state.increment}>+</button>
    </>
  )
})

/**
 * This demonstrates taking in props, using them observably within X.useState.
 * 
 * <ObservablePropsCounter multiplier={2.5} initialCount={0} />
 */
const ObservablePropsCounter = X<{ initialCount: number, multiplier: number }>((props) => {
  const state = X.useState(props, (props) => class {
    count = new Value(props.initialCount)
    get multipliedCount() {
      return this.count.value * props.multiplier // props.multiplier is observable!
    }

    increment = () => this.count.set(this.count.value + 1)
  })

  return (
    <>
      Count: {state.count.value}, Multiplied Count: {state.multipliedCount}
      <button onClick={state.increment}>+</button>
    </>
  )
})

Lifecycle Hooks

The goal of this library is to avoid using hooks from react during normal state management operations, thus the below lifecycle hooks are provided.

X.useOnMounted(() => {
  // Called when component mounts
})

X.useOnUnmounted(() => {
  // Called when component unmounts
})

X.useReaction(
  () => state.someValue,
  (newValue) => {
    // Called on first render, and whenever observable dependencies change
  }
)

X.useAutorun(() => {
  // Called on first render, and whenever observable dependencies change
})

Component Composition

In the below examples you can see how to create a Dialog component with Header and Body subcomponents.

const Dialog = X(({ children }) => (
  <div className={Dialog.classes.dialog} >{children}</div>
)).with({
  Header: X(({ children }) => (
    <header className={Dialog.classes.header} >{children}</header>
  )),
  Body: X(({ children }) => (
    <div className={Dialog.classes.body}>{children}</div>
  )),
  classes: {
    dialog: 'dialog',
    header: 'dialog-header',
    body: 'dialog-body',
  }
})

// Usage
<Dialog css={{
  // Can also ovveride using the classes we defined.
  [`.${Dialog.classes.dialog}`]: {
    background: 'white',
    padding: '1rem',
  }
}}>
  <Dialog.Header>Title</Dialog.Header>
  <Dialog.Body>Content</Dialog.Body>
</Dialog>

API

Core

• X<Props>() - Create an observed component with type support
• X.useState() - Create component-scoped state
• X.useOnMounted() - Mount lifecycle hook
• X.useOnUnmounted() - Unmount lifecycle hook
• X.useReaction() - MobX reaction hook
• X.useAutorun() - MobX autorun hook

Models

• Value<T> - Observable value container
• AsyncValue<T> - Async state container with pending/error/value states
• BoxedValue<T> - Encapsulated observable with custom getter/setter
• BoolValue - Boolean value with toggle utilities

Value

The Value class is effectively observable.box of interface { value: T, set: (value: T) => void }.

Features:

• Type inferrence
• Async mobx actions (no need to wrap in runInAction or use flow generators)
• Terseness
• Avoids reading value until necessary during prop-passing
• Supports two way binding patterns

const selectedFruit = new Value<'banana'|'apple'|undefined>(undefined)
selectedFruit.set('test') // TS error
selectedFruit.set('banana') // Valid
selectedFruit.value // 'banana'

AsyncValue

Think of react-query for this one. It is a Value that can be in a loading state, and can be awaited.

Features:

• Ergonomic types
• Async mobx actions
• Queuing
• Promise cancellation
• Pending state
• Error state
• Success state
• Progress state (eg. for uploads)

async function fetchFiles(c: { userId: string; foo: number }): Promise<{ name: string }[]> {
  return []
}

class ExampleModel {
  constructor() { makeAutoObservable(this) }
  activeUserId = '22'
  files = new AsyncValue(async ({ foo }: { foo: number }) =>
    fetchFiles({ userId: this.activeUserId, foo })
  )
}

const example = new ExampleModel()
example.files.value?.[0]?.name // undefined - missing data
await example.files.query({ foo: 22 }) // foo is strongly typed, inferred!
example.files.value?.[0]?.name // 'myFile.txt' - has data!
example.files.error // undefined - no error
example.files.isPending // false - we already awaited it

const v = new AsyncValue(() => fetchUsersList())
v.value // undefined
const promise = v.query() // Don't need to provide params as none are defined
v.isPending // true
await promise
v.isPending // false
v.value // [{ id: 1, name: 'John' }, { id: 2, name: 'Jane' }]

BoxedValue

Very similar to Value, however, allows for the getter and setter to be defined seperately, and additionally encapsulates the observable value inside the closure.

const blah = { something: 'banana' }

const somethingFromUri = new BoxedValue(
  // getter
  () => uriRoutes.someRoute.search.something,
  // setter
  (newValue) => uriRoutes.someRoute.push((uri) => ({ search: { something: newValue } })),
)

somethingFromUri.value // 'foo'
somethingFromUri.set('bar')
somethingFromUri.value // 'bar'

// Here we omit the setter, so the value is read-only
// This is effectively just a container encapsulating the value
const somethingWrappedToOptimizeObservability = new BoxedValue(
  () => blah.something,
)

somethingWrappedToOptimizeObservability.value // 'banana'
somethingWrappedToOptimizeObservability.set('banana') // does nothing, because no setter
  

BoolValue

A Value that is specifically for boolean values. It has a few additional methods to make working with booleans easier.

const isOpen = new BoolValue(true)

isOpen.toggle() // false
isOpen.toggle() // true
isOpen.setFalse()
isOpen.value // false
isOpen.isTrue // false
isOpen.setTrue()
isOpen.isTrue // true
isOpen.value // false

const Example = X(() => 
  <>
    <button onClick={isOpen.toggle}>Open</button>
    <Dialog onClose={isOpen.setFalse}>...</Dialog>
  </>
)

Documentation

• Extended Documentation and Examples
  • Further reading for advanced use cases, justifications etc.
• Conventions
  • Plug this into your AI instructions as prompts.

License

MIT