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operators.js
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operators.js
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/**
* @param {EventTarget} target
* @param {string} eventName
* @returns {ReadableStream}
*/
export function fromEvent (target, eventName) {
let _listener
return new ReadableStream({
start (controller) {
_listener = event => controller.enqueue(event)
target.addEventListener(eventName, _listener)
},
cancel () {
target.removeEventListener(eventName, _listener)
}
})
}
/**
* @param {number} milliseconds
* @returns {ReadableStream}
*/
export function interval (milliseconds) {
let _intervalId
return new ReadableStream({
start (controller) {
_intervalId = setInterval(() => {
controller.enqueue(Date.now())
}, milliseconds)
},
cancel () {
clearInterval(_intervalId)
}
})
}
/**
* @param {Function} callback
* @returns {TransformStream}
*/
export function map (callback) {
return new TransformStream({
transform (chunk, controller) {
controller.enqueue(callback.bind(callback)(chunk))
}
})
}
/**
* @typedef {ReadableStream | TransformStream} Stream
* @param {Stream[]} streams
* @returns {ReadableStream}
*/
export function merge (streams) {
return new ReadableStream({
async start (controller) {
/**
* @param {ReadableStreamDefaultReader} reader
* @returns {Promise<void>}
*/
async function read (reader) {
const { value, done } = await reader.read()
if (done || !controller.desiredSize) return
controller.enqueue(value)
return read(reader)
}
for (const stream of streams) {
const reader = (stream.readable || stream).getReader()
read(reader)
}
}
})
}
/**
* @typedef {function() : ReadableStream | TransformStream} StreamFunction
* @param {StreamFunction} callback
* @param {object} options
* @param {boolean} options.pairwise
* @returns {TransformStream}
*/
export function switchMap (callback, options = { pairwise: true }) {
return new TransformStream({
transform (chunk, controller) {
const stream = callback.bind(callback)(chunk)
const reader = (stream.readable || stream).getReader()
async function read () {
const { value, done } = await reader.read()
if (done) return
const result = options.pairwise ? [chunk, value] : value
controller.enqueue(result)
return read()
}
return read()
}
})
}
/**
* @param {ReadableStream | TransformStream} stream
* @returns {TransformStream}
*/
export function takeUntil (stream) {
/**
* @param {TransformStreamDefaultController<any>} controller
*/
async function readAndTerminate (controller) {
const reader = (stream.readable || stream).getReader()
const { value } = await reader.read()
controller.enqueue(value)
controller.terminate()
}
return new TransformStream({
start (controller) {
readAndTerminate(controller)
},
transform (chunk, controller) {
controller.enqueue(chunk)
}
})
}