promisify.ts

import fs = require('fs')

type NodeCallback<T> = (err:any, data:T) => void

/**
 * Accepts a function accepting a Node.js style callback, and calls it, returning a Promise
 */
const promisify = <T>(func:(cb:NodeCallback<T>) => void) =>
    new Promise<T>((resolve, reject) => {
        func((err, data) => {
            if (err) {
                reject(err)
            } else {
                resolve(data)
            }
        })
    })

const promisify0 = <T>(func:(cb:NodeCallback<T>) => void) =>
    () => promisify<T>(cb => func(cb))

const promisify1 = <P1, T>(func:(p1:P1, cb:NodeCallback<T>) => void) =>
    (p1:P1) => promisify<T>(cb => func(p1, cb))

const promisify2 = <P1, P2, T>(func:(p1:P1, p2:P2, cb:NodeCallback<T>) => void) =>
    (p1:P1, p2:P2) => promisify<T>(cb => func(p1, p2, cb))

const promisify3 = <P1, P2, P3, T>(func:(p1:P1, p2:P2, p3:P3, cb:NodeCallback<T>) => void) =>
    (p1:P1, p2:P2, p3:P3) => promisify<T>(cb => func(p1, p2, p3, cb))

const promisify4 = <P1, P2, P3, P4, T>(func:(p1:P1, p2:P2, p3:P3, p4:P4, cb:NodeCallback<T>) => void) =>
    (p1:P1, p2:P2, p3:P3, p4:P4) => promisify<T>(cb => func(p1, p2, p3, p4, cb))









async function test1():Promise<void> {
    let fd = await promisify<number>(cb => fs.open('foo.txt', 'w', 'mode', cb))
    // ...
    await promisify<void>(cb => fs.close(fd, cb))
}

async function test2():Promise<void> {
    let fd = await promisify3(fs.open)('foo.txt', 'w', 'mode')
    // ...
    await promisify1(fs.close)(fd)
}