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, because reactronic takes full care of tracking dependencies between visual components (observers) and state (observable objects).

Transactional reactivity is based on four fundamental concepts:

• Observable Objects - a set of objects that store data of an application (state);
• Transactional Function - makes changes in observable objects in atomic way ("all or nothing");
• Reactive Function - is executed automatically in response to changes made by a transaction;
• Cached Function - its result is remembered and, if the becomes obsolete, recomputed 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 ObservableObject {
  name: string = 'Nezaboodka Software'
  email: string = 'contact@nezaboodka.com'

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

  @reactive
  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, printContact function depends on name and email fields. It is executed automatically in response to changes of these fields made by saveContact function.

Here is an example of cached value (re-)computed on-demand:

class Demo extends ObservableObject {
  name: string = 'Nezaboodka Software'
  email: string = 'contact@nezaboodka.com'

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

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

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

Observable Objects

Observable objects 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 ObservableObject {
  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 ObservableObject class and all its properties url, content, and timestamp are hooked.

Transactional Functions

Transactional function makes changes in observable objects in transactional (atomic) way. Such a function is instrumented with hooks to provide transparent atomicity (by implicit context switching and isolation).

class MyModel extends ObservableObject {
  // ...
  @transactional
  async load(url: string): Promise {
    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 transaction is running, the changes are visible only inside the transaction itself. The new values become atomically visible outside of the transaction only upon its completion.

Atomicity is achieved by making changes in an isolated data snapshot that is not visible outside of the running transaction 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 transaction. 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 the transaction failure, because all the changes made by the transaction in its logical snapshot are simply discarded. In case the transaction is successfully applied, affected caches 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 transaction execution. The transaction may consist of a set of asynchronous calls prolonging the transaction until completion of all of them. An asynchronous call may spawn other asynchronous calls, which prolong transaction 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 made by a transaction in observable objects. Cached function is called on-demand to renew the value if it was marked as obsolete due to changes made by a transaction. Reactive and cached functions are instrumented with hooks to seamlessly subscribe to those observable objects and other cached functions (dependencies), which are used during their execution.

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

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

  @reactive // called immediately in response to changes
  ensureUpToDate(): void {
    if (this.shouldComponentUpdate())
      Transaction.outside(() =&gt; this.setState({})) // ask React to re-render
  } // ensureUpToDate is subscribed to render

  shouldComponentUpdate(): boolean {
    return !RxSystem.getController(this.render).isUpToDate
  }

  componentDidMount(): void {
    this.ensureUpToDate() // run to subscribe for the first time
  }

  componentWillUnmount(): void {
    Transaction.run(null, RxSystem.dispose, this)
  }
}

In the example above, reactive function refresh is transparently subscribed to the cached function render. In turn, the render function is subscribed to the url and content properties of a corresponding MyModel object. Once url or content values are changed, the render cache becomes obsolete and causes the refresh function to become obsolete as well and re-executed. While being executed, the refresh function enqueues re-rendering request to React, which calls render function 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 observable objects and other cached functions 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 observable objects and reactive/cached functions. With Reactronic, you no longer need to create data change events in one set of objects, subscribe 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 transaction is applied (synchronously);
• 0 - execute immediately via event loop (asynchronously with zero timeout);
• >= Number.MAX_SAFE_INTEGER - never execute (suspended reactive function).

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);
• Asynchrony, 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 TransactionalObject { }
class ObservableObject { }

// Decorators & Operators

function raw(proto, prop) // field only
function transaction(proto, prop, pd) // method only
function reactive(proto, prop, pd) // method only
function cached(proto, prop, pd) // method only
function options(value: Partial): F

function unobs(func: F, ...args: any[]): T
function sensitive(sensitivity: Sensitivity, func: F, ...args: any[]): T

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

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

type MemberOptions = {
  readonly kind: Kind
  readonly isolation: Isolation
  readonly order: number
  readonly noSideEffects: boolean
  readonly triggeringArgs: 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
}

enum Kind {
  plain = 0,
  transactional = 1,
  reactive = 2,
  cached = 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
  readonly busyDuration: number
  abstract whenBusy(): Promise
  abstract whenIdle(): Promise
  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
}

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 = (...args: any[]) => T

class Transaction implements Worker {
  static readonly current: Transaction

  readonly id: number
  readonly hint: string

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

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

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

// Controller

abstract class Controller {
  readonly options: Options
  readonly args: ReadonlyArray
  readonly value: T
  readonly error: any
  readonly stamp: number
  readonly isUpToDate: boolean

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

// Reactronic

class Reactronic {
  static why(short: boolean = false): string
  static getMethodCache(method: F): Cache
  static configureCurrentOperation(options: Partial): Options
  static getRevisionOf(obj: any): number
  static takeSnapshot(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(obj: T, name: string | undefined): void
  static getLoggingHint(obj: T): string | undefined
  static setProfilingMode(isOn: boolean, options?: Partial): void
}

Contribution

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