audit

Audit operator based on a trigger stream. Only emits the latest resolved value from the source stream when the trigger is activated.

Type Definition

type audit = <T>(
  trigger$: Stream | Observable,
  shouldAwait?: boolean
) => (observable$: Observable<T>) => Observable<T>

Parameters

• trigger$ (Stream | Observable): The trigger stream. When this stream emits a value, the audit operator emits the latest resolved value from the source stream.
• shouldAwait (boolean, optional): Whether to wait for the source stream's pending state to resolve. Defaults to true. If the source is pending when triggered, it will wait for resolution before emitting.

Return Value

Returns a new Observable that only emits the latest resolved value from the source stream when the trigger is activated.

Details

• Only emits the current value of the source stream when the trigger stream emits a value.
• Only emits resolved values, ignores rejected Promises.
• If the source stream emits multiple values quickly, only the latest resolved value is emitted.
• When shouldAwait is true, if the source is pending, it waits for resolution before emitting.
• When the trigger$ stream completes, the stream produced by audit also completes.

Usage Scenarios

Scenario 1: Basic trigger emission

import { $, audit } from 'fluth'

const source$ = $()
const trigger$ = $()

const audited$ = source$.pipe(audit(trigger$))

audited$.then((value) => {
  console.log('audited:', value)
})

// Set values on the source stream, but they are not emitted immediately
source$.next(1)
source$.next(2)
source$.next(3)

// Only emits the latest value when the trigger is activated
trigger$.next('trigger') // Output: audited: 3

Scenario 2: Handling rapidly changing data

import { $, audit } from 'fluth'

const searchInput$ = $()
const searchTrigger$ = $()

const searchResults$ = searchInput$.pipe(audit(searchTrigger$))

searchResults$.then((keyword) => {
  console.log('Search keyword:', keyword)
})

// User types quickly
searchInput$.next('a')
searchInput$.next('ap')
searchInput$.next('app')
searchInput$.next('apple')

// Only emits the latest search keyword when triggered
searchTrigger$.next('search') // Output: Search keyword: apple

Scenario 3: Awaiting asynchronous values

import { $, audit } from 'fluth'

const source$ = $()
const trigger$ = $()

// shouldAwait is true (default)
const audited$ = source$.pipe(audit(trigger$, true))

audited$.then((value) => {
  console.log('audited:', value)
})

// Send a Promise that resolves after some time
const slowPromise = new Promise((resolve) => {
  setTimeout(() => resolve('async result'), 1000)
})
source$.next(slowPromise)

// Trigger immediately, but will wait for the Promise to resolve
trigger$.next('trigger')
// After 1 second: Output: audited: async result

Scenario 4: Not awaiting asynchronous values

import { $, audit } from 'fluth'

const source$ = $()
const trigger$ = $()

// shouldAwait is false
const audited$ = source$.pipe(audit(trigger$, false))

audited$.then((value) => {
  console.log('audited:', value)
})

const slowPromise = new Promise((resolve) => {
  setTimeout(() => resolve('async result'), 1000)
})
source$.next(slowPromise)

// Trigger immediately, does not wait for the Promise to resolve
trigger$.next('trigger') // Output: audited: undefined