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@shmish/observable

ESM ES observable module, for personal use

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@shmish/observable

npm install @shmish/observable --save

Usage

Observable

An observable is an object that represents a collection of values arriving syncrounously or asyncrounously. Using this constructor directly is not recomended unless absolutly nessasarry. In practice, it is almost always better to use one of the static creation methods such as Observable.fromEvent and Observable.of

// Example
const myObservable = new Observable(observer => {
  setInterval(observer.next, 1000, 'some data')
})

Observable.of(...args)

Observable.of takes any number of arguments and returns a new Observable collection of the arguments (in order).

// Example
const myFirstObservable = Observable.of(2, 4, 6)
const mySecondObservable = Observable.of('hello', 3, 56, 0x10)

Observable.from(iterable)

Observable.from takes a single iterable as an argument, such as a String, Array, or Generator and returns a new Observable collection of the itterable argument.

// Example
const myFirstObservable = Observable.from([1, 2, 4])
const MySecondObservable = Observable.from('hello world')

Observable.fromEvent(emiter, ...events)

Observable.fromEvent takes an event emitter (implements on or addEventListener) and any number of events to subscribe to. The Observable will automaticly notify any attached observers when an event is triggered.

// Example
const $button = document.getElementById('button')
const clickStream = Observable.fromEvent($button, 'click', 'touch')

Observable.prototype.subscribe(observer | [functions])

Observable.prototype.subscribe takes either an Observer object or a next, error, and complete callback (in that order). .subscribe returns a Subscription object, representing the data channel between the Observable collection and the Observer

// Example: callbacks
const subsription = Observable.of(1, 2, 3).subscribe(
  val => console.log(val),     // Next
  err => console.error(err),   // Error
  () => console.log('done')    // Complete
)

//=> 1
//=> 2
//=> 3
//=> 'done'
// Example: Observer
// Note: all overrides are optional
class Logger extends Observer {
  next (val) { console.log(val) }  // Override 'next' method
  error (err) { console.error(err) }  // Override 'error' method
  complete () { console.log('done') }  // Override 'complete' method
}

const subscription = Observable.of(1, 2, 3).subscribe(new Logger())

//=> 1
//=> 2
//=> 3
//=> 'done'

Observable.prototype.map(functor)

The Observable.prototype.map method creates a new Observable with the results of calling the provided function on each value passing through the calling Observable

// Example
const subscription = Observable.of(1, 2, 3)
  .map(x => x ** 2)
  .map(x => x - 1)
  .subscribe(x => console.log(x))

//=> 0
//=> 3
//=> 8


// Another example
const subscription = Observable.from('hello')
  .map(c => c.toUpperCase())
  .subscribe(c => console.log(c))

//=> 'H'
//=> 'E'
//=> 'L'
//=> 'L'
//=> 'O'

Observable.prototype.filter(functor)

The Observable.prototype.filter method creates a new Observable with all the elements that pass the test of the provided function

// Example
const subscription = Observable.of(1, 2, 3, 4)
  .filter(x => x % 2 === 0)
  .subscribe(x => console.log(x))

//=> 2
//=> 4

Observable.prototype.reduce(functor, [initial])

The Observable.prototype.reduce method return a Promise of the value resulting from applying the provided function against an accumulatorand each element passing throught the observable. The function takes the form of (accumulator, value) => newVal

// Example
const myPromise = Observable.of(1, 2, 3)
  .reduce((acc, val) => acc + val)

//=> Promise {val: 6}

// Another example
Observable.of(1, 2, 3)
  .reduce((acc, val, i) => acc + val + i)  // Here, an optional index param is passed
  .then(x => console.log(x))

//=> 9

Observable.prototype.wait(delayMS)

The Observable.prototype.wait method produces a new Observable that 'holds' values for a provided delay before parring them on.

// Example
Observable.of(1, 2, 3)
  .wait(200)
  .subscribe(x => console.log(x))

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