Reactronic - Transactional Reactive State Management

Reactronic is an experimental JavaScript library that provides transactional reactive state management in a Web application.

Transactional reactivity means that state changes are being made in an isolated data snapshot and then, once atomically applied, are consistently propagated to corresponding visual components for (re)rendering. All that is done in automatic, seamless, and fine-grained way. Reactronic takes full care of tracking dependencies between visual components (reactive functions) and application state (signalling objects).

Transactional reactivity is based on four fundamental concepts:

• Signalling Objects - a set of objects that store data of an application (state) and cause reactions upon their changes;
• Transactional Function - a function that makes changes in signalling objects in atomic way ("all or nothing");
• Reactive Function - a function that is (re-)executed in response to changes made in signalling objects by transactional functions;
• Cache Function - a function which result is remembered and, if becomes obsolete, causes function to re-execute on-demand.

Demo application built with Reactronic: https://nevod.io/#/playground. Source code of the demo: https://gitlab.com/nezaboodka/nevod.web.public/-/blob/master/README.md.

Quick introduction and detailed description is below.

Quick Introduction

Here is an example of transactional reactive code:

class Demo extends RxObject {
  name: string = 'Nezaboodka Software'
  email: string = '[email protected]'

  @transaction
  saveContact(name: string, email: string): void {
    this.name = name
    this.email = email
  }

  @reaction
  printContact(): void {
    // depends on `name` and `email` and reacts to their changes
    if (this.email.indexOf('@') >= 0)
      throw new Error(`wrong email ${this.email}`)
    console.log(this.name + ' <' + this.email + '>')
  }
}

In the example above, Demo is a signalling object, meaning that access to its fields are seamlessly tracked to determine dependent reactive and cached functions. Reactive function printContact reads name and email fields, thus depends on them. It is executed automatically in response to changes of these fields made by the transactional function saveContact.

Here is an example of a cached result that is (re-)computed on-demand:

class Demo extends SignallingObject {
  name: string = 'Nezaboodka Software'
  email: string = '[email protected]'

  @cache
  get contact(): string {
    return this.name + ' <' + this.email + '>'
  }

  @reaction
  printContact(): void {
    if (this.contact !== '')
      Console.log(this.contact)
  }
}

In the example above, the result of contact getter is computed from source fields name and email. Once computed, the result is cached and is reused until source fields name and email are changed. Once source fields changed, contact result becomes obsolete, thus causing execution of depending reactive function printContact. When function of reactive function printContact runs it reads contact and causes its re-computation.

Signalling Objects

Signalling objects are aimed to store data of an application. All such objects are transparently hooked to track access to their properties, both on reads and writes.

class MyModel extends RxObject {
  url: string = "https://github.com/nezaboodka/reactronic"
  content: string = "transactional reactive state management"
  timestamp: Date = Date.now()
}

In the example above, the class MyModel is based on Reactronic's RxObject class and all its properties url, content, and timestamp are hooked.

Transactional Function

Transactional function makes changes in signalling objects in atomic way ("all or nothing"), thus provoking execution of dependent reactive and cached functions. Transactional function is instrumented with hooks to provide transparent atomicity (by implicit context switching and isolation).

class MyModel extends RxObject {
  // ...
  @transaction
  async load(url: string): Promise<void> {
    this.url = url
    this.content = await fetch(url)
    this.timestamp = Date.now()
  }
}

In the example above, the transactional function load makes changes to url, content and timestamp properties. While transactional function is running, the changes are visible only inside the function itself. The new values become atomically visible outside of the function only upon its completion.

Atomicity is achieved by making changes in an isolated data snapshot that is not visible outside of the running function until it is fully finished and applied. Multiple objects and their properties can be changed with full respect to the all-or-nothing principle. To do so, separate data snapshot is automatically maintained for each transactional function. That is a logical snapshot that does not create a full copy of all the data.

Compensating rollback operations are not needed in case of a transactional function failure, because all the changes made by transactional function in its logical snapshot are simply discarded. In case a transaction function is successfully applied, affected cached results are marked as obsolete and corresponding caching functions are re-executed in a proper order (but only when all the data changes are fully applied).

Asynchronous operations (promises) are supported out of the box during transactional function execution. Transactional function may consist of a set of asynchronous calls prolonging the function until completion of all of them. An asynchronous call may spawn other asynchronous calls, which prolong transactional execution until the whole chain of asynchronous operations is fully completed.

Reactive & Cached Functions

Reactive function is automatically and immediately called in response to changes in signalling objects made by transactional functions. Cached function is called on-demand to renew the result if it was marked as obsolete due to changes made by an transactional functions. Reactive and cached functions are instrumented with hooks to seamless listening of those signalling objects and other cached functions (dependencies), which are used during their execution.

class MyView extends Component<{model: MyModel}> {
  @cache
  render(): React.JSX.Element {
    return (
      <div>
        <h1>{this.props.model.url}</h1>
        <div>{this.props.model.content}</div>
      </div>
    )
  } // render is listening to "url" and "content"
}

class Component<P> extends React.Component<P> {
  @cache
  render(): React.JSX.Element {
    throw new Error('render method is undefined')
  }

  @reaction // called in response to changes
  ensureUpToDate(): void {
    if (this.shouldComponentUpdate()) {
      // Ask React to re-render
      Transaction.outside(() => this.setState({}))
    }
  } // EnsureUpToDate is listening to render

  shouldComponentUpdate(): boolean {
    const r = manageReaction(this.render)
    return !r.isUpToDate
  }

  componentDidMount(): void {
    // Run for the first time to start listening
    this.ensureUpToDate()
  }

  componentWillUnmount(): void {
    runTransactional(disposeRxObject, this)
  }
}

In the example above, reactive function refresh transparently listens to the cached function render. In turn, cached function render listens to the properties url and content of a corresponding MyModel object. Once url or content values are changed, the cached function render becomes obsolete and causes the reactive function refresh to become obsolete and re-executed. While being executed, the reactive function refresh enqueues re-rendering request to React, which calls cached function render causing it to renew its cached value.

In general case, all reactive and cached functions are automatically and immediately marked as obsolete when changes are made in those signalling objects and other cached results that were used during their execution. And once marked, the functions are automatically executed again, either immediately (for reactive functions) or on-demand (for cached functions).

Reactronic takes full care of tracking dependencies between all the signalling objects and reactive/cached functions. With Reactronic, you no longer need to create data change events in one set of objects, listen to these events in other objects, and manually maintain switching from the previous object version to a new one.

Behavior Options

There are multiple options to configure behavior of transactional reactivity.

Order options defines order of execution for reactive functions:

• (TBD)

Throttling option defines how often reactive function is executed in case of recurring changes:

• (ms) - minimal delay in milliseconds between executions;
• -1 - execute immediately once transactional function changes are applied (synchronously);
• 0 - execute immediately via event loop (asynchronously with zero timeout);
• >= Number.MAX_SAFE_INTEGER - never execute (suspended reaction).

Reentrance option defines how to handle reentrant calls of transactional and reactive functions:

• preventWithError - fail with error if there is an existing call in progress;
• waitAndRestart - wait for previous call to finish and then restart current one;
• cancelPrevious - cancel previous call in favor of recent one;
• cancelAndWaitPrevious - cancel previous call in favor of recent one (but wait until canceling is completed)
• runSideBySide - multiple simultaneous calls are allowed.

Indicator is an object that maintains status of running functions, which it is attached to. A single indicator object can be shared between multiple transactional, reactive, and cached functions, thus maintaining consolidated status for all of them (busy, workers, etc).

Notes

Inspired by: MobX, Nezaboodka, Excel.

Key Reactronic principles and differentiators:

• No compromises on consistency, clarity, and simplicity;
• Minimalism and zero boilerplating (it's not a framework bloating your code);
• Async, patches, undo/redo, conflict resolving are provided out of the box;
• Seamless integration with transactional reactive object-oriented databases like Nezaboodka;
• Compact dependency-free implementation consisting of less than 2K lines of code.

Roadmap:

• Patches and conflict resolution API (partially done)
• History/undo/redo API and implementation (partially done)
• Sync API and implementation (not implemented yet)

Installation

NPM: npm install reactronic

API (TypeScript)

// Classes

class TxObject { } // transactional object
class RxObject { } // reactive object

// Decorators & Operators

function signal(boolean) // field only
function signal(proto, prop) // field only
function transaction(proto, prop, pd) // method only
function reaction(proto, prop, pd) // method only
function cache(proto, prop, pd) // method only
function options(value: Partial<ReactivityOptions>): F<any>

function runNonReactive<T>(func: F<T>, ...args: any[]): T
function runSensitive<T>(sensitivity: Sensitivity, func: F<T>, ...args: any[]): T

// SnapshotOptions, ReactivityOptions, Kind, Reentrance, Indicator, LoggingOptions, ProfilingOptions

export type SnapshotOptions = {
  readonly hint?: string
  readonly isolation?: Isolation
  readonly journal?: Journal
  readonly logging?: Partial<LoggingOptions>
  readonly token?: any
}

type ReactivityOptions = {
  readonly kind: Kind
  readonly isolation: Isolation
  readonly order: number
  readonly noSideEffects: boolean
  readonly signalArgs: boolean
  readonly throttling: number // milliseconds, -1 is immediately, Number.MAX_SAFE_INTEGER is never
  readonly reentrance: Reentrance
  readonly journal: Journal | undefined
  readonly indicator: Indicator | null
  readonly logging?: Partial<LoggingOptions>
}

enum Kind {
  plain = 0,
  transaction = 1,
  reaction = 2,
  cache = 3
}

enum Reentrance {
  preventWithError = 1, // fail with error if there is an existing call in progress (default)
  waitAndRestart = 0, // wait for existing call to finish and then restart current one
  cancelPrevious = -1, // cancel previous call in favor of recent one
  cancelAndWaitPrevious = -2, // cancel previous call in favor of recent one (but wait until canceling is completed)
  overwritePrevious = -2, // allow previous to complete, but overwrite it with ignoring any conflicts
  runSideBySide = -3 // multiple simultaneous calls are allowed
}

class Indicator {
  readonly isBusy: boolean
  readonly counter: number
  readonly workers: ReadonlySet<Worker>
  readonly busyDuration: number
  abstract whenBusy(): Promise<void>
  abstract whenIdle(): Promise<void>
  static create(hint: string, activationDelay: number, deactivationDelay: number): Indicator
}

type Worker = {
  readonly id: number
  readonly hint: string
  isCanceled: boolean
  isFinished: boolean
  cancel(error?: Error, retryAfter?: Transaction): this
  whenFinished(): Promise<void>
}

type LoggingOptions = {
  readonly off: boolean
  readonly transaction: boolean
  readonly operation: boolean
  readonly step: boolean
  readonly indicator: boolean
  readonly read: boolean
  readonly write: boolean
  readonly change: boolean
  readonly obsolete: boolean
  readonly error: boolean
  readonly warning: boolean
  readonly gc: boolean
}

type ProfilingOptions = {
  repetitiveUsageWarningThreshold: number // default: 10 times
  mainThreadBlockingWarningThreshold: number // default: 16.6 ms
  asyncActionDurationWarningThreshold: number // default: 150 ms
}

// Transaction

type F<T> = (...args: any[]) => T

class Transaction implements Worker {
  static readonly current: Transaction

  readonly id: number
  readonly hint: string

  run<T>(func: F<T>, ...args: any[]): T
  wrap<T>(func: F<T>): F<T>
  apply(): void
  seal(): this // a1.seal().whenFinished().then(fulfill, reject)
  cancel(error?: Error, retryAfter?: Transaction): this
  isCanceled: boolean
  isFinished: boolean
  whenFinished(): Promise<void>
  join<T>(p: Promise<T>): Promise<T>

  static create(options: SnapshotOptions | null): Transaction
  static run<T>(options: SnapshotOptions | null, func: F<T>, ...args: any[]): T
  static off<T>(func: F<T>, ...args: any[]): T

  static isFrameOver(everyN: number, timeLimit: number): boolean
  static requestNextFrame(sleepTime: number): Promise<void>
  static isCanceled: boolean
}

// Reaction

abstract class Reaction<T> {
  readonly options: Options
  readonly args: ReadonlyArray<any>
  readonly value: T
  readonly error: any
  readonly stamp: number
  readonly isReusable: boolean

  configure(options: Partial<Options>): Options
  markObsolete(): boolean
  pullLastResult(args?: any[]): T | undefined
}

// ReactiveSystem

class ReactiveSystem {
  static why(short: boolean = false): string
  static getMethodCache<T>(method: F<T>): Cache<T>
  static configureCurrentReaction(options: Partial<Options>): Options
  static getRevisionOf(obj: any): number
  static takeSnapshot<T>(obj: T): T
  static dispose(obj: any): void
  static reactivityAutoStartDisabled: boolean
  static readonly isLogging: boolean
  static readonly loggingOptions: LoggingOptions
  static setLoggingMode(isOn: boolean, options?: LoggingOptions)
  static setLoggingHint<T extends object>(obj: T, name: string | undefined): void
  static getLoggingHint<T extends object>(obj: T): string | undefined
  static setProfilingMode(isOn: boolean, options?: Partial<ProfilingOptions>): void
}

Contribution

By contributing, you agree that your contributions will be automatically licensed under the Apache 2.0 license (see LICENSE file).