$ Function

$ is the factory function for Stream, used to create a stream. It is one of the most commonly used functions in the fluth library, similar to Promise.resolve() but supports continuous data emission.

Type Definition

export function $<T = any>(): Stream<T, false>
export function $<T = any>(data: T): Stream<T, true>
export function $<T = any>(data?: T) {
  return new Stream<T, boolean>(data)
}

Parameters

• data (optional): Initial data for the stream
  • If no parameter is passed, an empty stream is created, and value type is T | undefined
  • If data is passed, a stream with an initial value is created, and value type is T

Return Value

Returns a Stream instance, which inherits from Observable and has the following features:

• Can actively emit data (via next method)
• Supports immutable data updates (via set method)
• Supports chainable operations (via then method)
• Supports operators (via pipe method)
• Supports plugin system (via use method)

Usage Scenarios

1. Create an empty stream

import { $ } from 'fluth'

// Create an empty stream, initial value is undefined
const stream$ = $()
console.log(stream$.value) // undefined

// Subscribe to data changes
stream$.then((data) => {
  console.log('Received data:', data)
})

// Emit data
stream$.next('hello') // Output: Received data: hello
stream$.next('world') // Output: Received data: world

2. Create a stream with initial value

import { $ } from 'fluth'

// Create a stream with initial value
const stream$ = $('Initial Value')
console.log(stream$.value) // "Initial Value"

// Subscribe to data changes
stream$.then((data) => {
  console.log(data) // Output: Initial Value
})

// Continue to emit new data
stream$.next('New Data') // Output: New Data

3. Create a stream of complex objects

import { $ } from 'fluth'

// Create an object stream
const user$ = $({ name: 'Tom', age: 25, address: { city: 'Beijing' } })

// Subscribe to user info changes
user$.then((user) => {
  console.log('User info:', user)
})

// Use set method for immutable update
user$.set((user) => {
  user.age = 26
  user.address.city = 'Shanghai'
})

Notes

1. Type inference: TypeScript will automatically infer the stream type based on the data type passed in
2. Immutability: When using the set method, fluth will automatically create immutable objects to maintain reference equality
3. Chainable operations: The returned stream supports chainable operations similar to Promise

Complete Example

import { $, combine, consoleNode } from 'fluth'

// Create multiple streams
const name$ = $('Tom')
const age$ = $(25)
const city$ = $('Beijing')

// Combine streams
const user$ = combine(name$, age$, city$)

// Subscribe and process
user$.then(([name, age, city]) => {
  console.log(`User: ${name}, Age: ${age}, City: ${city}`)
})

// Update data
name$.next('Jerry')
age$.next(30)
city$.next('Shanghai')

// Output: User: Jerry, Age: 30, City: Shanghai