Function first

first<T>(...coros): Generator<any, T, unknown>

Returns a coroutine that waits for the first coroutine of coros to complete.

When waited on with yield* returns the value returned by the first completed coroutine. All other coroutines are cancelled with Generator.return, triggering their finally handlers if any.

Type Parameters

T
Return type of all coros and as a result this coroutine

Parameters

Rest ...coros: Coroutine<T>[]
The coroutines to wait for

Returns Generator<any, T, unknown>

A generator that returns the value returned by first completed coroutine

See

Generator.return

Example: Interrupt infinite coroutine

import * as coro from '@ajeeb/coroutines'

function* printForever(message) {
     while(true) {
         console.log(message)
         yield* seconds(1)
     }
}

function* waitForClick() {
     let pressed = false
     const button = document.querySelector("button")
     button.onclick = () => pressed = true
     while(!pressed) yield
}

const SCHED = new coro.Schedule()
SCHED.add(coro.first(printForever("ping"), waitForClick()))
setInterval(SCHED.tick, 100)

Example: Get first pressed button

import * as coro from '@ajeeb/coroutines'

function* waitForClick(button) {
     let pressed = false
     button.onclick = () => pressed = true
     while(!pressed) yield
     return button.textContent
}

const buttons = Array.prototype.slice.call(document.querySelectorAll("button"))
const SCHED = new coro.Schedule()
SCHED.add(function* () {
     console.log("waiting for button press...")
     const pressedText = yield* coro.first(...buttons.map(waitForClick))
     console.log("pressed", pressedText)
})
setInterval(SCHED.tick, 100)