@rse/observable v0.9.0

@rse/observable

Observable Objects for TypeScript

About

This is a small TypeScript library for making a data structure "observable" in order to let registered "observer" functions called in case of any modifications to the data structure. The key design criterias for this library are: simple API, TypeScript type safety, and support for objects of the standard types Object, Array, Typed Arrays, Map/WeakMap, and Set/WeakSet.

Installation

$ npm install --save @rse/observable

API

type Observer<T extends object> = {
    pause(): void
    resume(): void
    destroy(): void
};
type Observation<T extends object> = {
    type: "change" | "delete"
    target: T
    path: string
    valueNew: any | undefined
    valueOld: any | undefined
};
type ObservationCallback<T extends object> =
    (observation: Observation<T>) => void

declare function observable<T extends object>(obj: T, strict?: boolean): T
declare function observer<T extends object>(observable: T, callback: ObservationCallback<T>): Observer<T>

declare function isObservable(object: object): boolean
declare function raw<T extends object>(observable: T): T

Example

Code:

import { observable, observer } from "@rse/observable"

const obj = observable({
    a: 1,
    b: { b1: { b2: { b3: "foo" } } },
    c: [ 7, 42, [ 1, 2, 3 ] ],
    d: new Set<number | number[]>([ 7, 42, [ 1, 2, 3 ] ]),
    e: new Map<string, number | number[]>([ [ "g1", 7 ], [ "g2", 42 ], [ "g3", [ 1, 2, 3 ]] ]),
    f: new Uint8Array([ 0x01, 0x02, 0x03 ])
})

observer(obj, (observation) => {
    console.log(observation)
})
observer(obj.b.b1, (observation) => {
    console.log(observation)
})

obj.a = 2
obj.b.b1.b2.b3 = "bar"
delete obj.c[2]
obj.d.add(7)
obj.e.set("g4", 0)
obj.f.fill(0x07, 1, 3)

Output:

{
  type: 'change',
  target: {
    a: 2,
    b: { b1: [Object] },
    c: [ 7, 42, [Array] ],
    d: Set(3) { 7, 42, [Array] },
    e: Map(3) { 'g1' => 7, 'g2' => 42, 'g3' => [Array] },
    f: Uint8Array(3) [ 1, 2, 3 ]
  },
  path: 'a',
  valueNew: 2,
  valueOld: 1
}
{
  type: 'change',
  target: { b2: { b3: 'bar' } },
  path: 'b2.b3',
  valueNew: 'bar',
  valueOld: 'foo'
}
{
  type: 'change',
  target: {
    a: 2,
    b: { b1: [Object] },
    c: [ 7, 42, [Array] ],
    d: Set(3) { 7, 42, [Array] },
    e: Map(3) { 'g1' => 7, 'g2' => 42, 'g3' => [Array] },
    f: Uint8Array(3) [ 1, 2, 3 ]
  },
  path: 'b.b1.b2.b3',
  valueNew: 'bar',
  valueOld: 'foo'
}
{
  type: 'delete',
  target: {
    a: 2,
    b: { b1: [Object] },
    c: [ 7, 42, <1 empty item> ],
    d: Set(3) { 7, 42, [Array] },
    e: Map(3) { 'g1' => 7, 'g2' => 42, 'g3' => [Array] },
    f: Uint8Array(3) [ 1, 2, 3 ]
  },
  path: 'c.2',
  valueNew: undefined,
  valueOld: [ 1, 2, 3 ]
}
{
  type: 'change',
  target: {
    a: 2,
    b: { b1: [Object] },
    c: [ 7, 42, <1 empty item> ],
    d: Set(3) { 7, 42, [Array] },
    e: Map(3) { 'g1' => 7, 'g2' => 42, 'g3' => [Array] },
    f: Uint8Array(3) [ 1, 2, 3 ]
  },
  path: 'd.*',
  valueNew: 7,
  valueOld: undefined
}
{
  type: 'change',
  target: {
    a: 2,
    b: { b1: [Object] },
    c: [ 7, 42, <1 empty item> ],
    d: Set(3) { 7, 42, [Array] },
    e: Map(4) { 'g1' => 7, 'g2' => 42, 'g3' => [Array], 'g4' => 0 },
    f: Uint8Array(3) [ 1, 2, 3 ]
  },
  path: 'e.g4',
  valueNew: 0,
  valueOld: undefined
}
{
  type: 'change',
  target: {
    a: 2,
    b: { b1: [Object] },
    c: [ 7, 42, <1 empty item> ],
    d: Set(3) { 7, 42, [Array] },
    e: Map(4) { 'g1' => 7, 'g2' => 42, 'g3' => [Array], 'g4' => 0 },
    f: Uint8Array(3) [ 1, 7, 7 ]
  },
  path: 'f.1',
  valueNew: Uint8Array(2) [ 7, 7 ],
  valueOld: Uint8Array(2) [ 2, 3 ]
}

History

The @rse/observable library was implemented in May 2025 for potential use in the SpeechFlow application.

Support

The work on this Open Source Software was financially supported by the german non-profit organisation SEA Software Engineering Academy gGmbH.

License

Copyright © 2025 Dr. Ralf S. Engelschall (http://engelschall.com/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.