Cancellable Promises

cancellable-promises

#!/usr/bin/env node

class CancelError extends Error {
    constructor(message) {
        super(message)
        this.name = 'CancelError'
    }
}

function random(minimum, maximum) {
    return minimum + Math.floor(Math.random() * (maximum - minimum + 1))
}

function sleep(signal) {
    return new Promise((resolve, reject) => {
        const timeout = setTimeout(
            resolve,
            random(250, 750),
            random(0, 1) ? 'z' : 'Z'
        )

        signal.cancel = () => {
            clearTimeout(timeout)
            reject(new CancelError('\\(´O`)/'))
        }
    })
}

async function main() {
    const signal = {
        cancel: () => {}
    }

    setTimeout(
        () => signal.cancel(),
        random(2500, 7500)
    )

    try {
        while (true) {
            console.log(await sleep(signal))
        }
    } catch(exception) {
        if (exception instanceof CancelError) {
            console.log(exception.message)
            return
        }

        throw exception
    }
}

main()

cancellable-promises.md

Cancellable Promises