makepromise

makepromise

Make native Promise from function with callback.

ES5

The package uses some newer language features. For your convenience, it's been transpiled to be compatible with Node 4. You can use the following snippet.

const makePromise = require('makepromise/es5/src/')

makePromise(fn:Function(...args, cb:Function(err:Error, res:any))) => Promise<any>

Create a promise from a function which accepts a callback as the last argument, and where the callback will be called with 2 arguments: (error, result).

For example, you can unlink a file (here, a temp file is created with wrote package):

const { unlink } = require('fs')
const { createWritable } = require('wrote')
const makePromise = require('makepromise')

let file
(async () => {
    // create a temp file and open a writable stream
    const ws = await createWritable()

    const { path: file } = ws // /var/folders/s0/tmp/T/wrote-69822.data

    // here, just close the stream without makepromise, because it's a different
    // kind of constructor, ie. resolve-reject and not error callback handlers
    await new Promise((resolve, reject) => {
        ws.once('close', resolve)
        ws.once('error', reject)
        ws.close()
    })
    await makePromise(unlink, file)
})()

In addition, errors will be updated to include the stack trace of when makePromise was called, rather than have node internal error stack, or no stack at all:

const fs = require('fs')
const makePromise = require('makepromise');

(async () => {
    try {
        await makePromise(fs.unlink, 'error-test-file')
    } catch ({ stack }){
        console.log(stack)
        /*
        Error: ENOENT: no such file or directory, unlink 'error-test-file'
            at cb (makepromise/src/index.js:28:31)
            at makePromise (makepromise/src/index.js:18:16)
            at Object.<anonymous> (makepromise/examples/error-stack.js:4:1)
        */

        // without this feature:
        /*
        Error: ENOENT: no such file or directory, unlink 'error-test-file'
        */
    }
})()

makePromise(fn:Function(...args, cb:Function(err:Error, res:any), resolveValue:any)) => Promise<any>

Pass resolveValue as second argument to make promise be resolved with it.

const { unlink } = require('fs')
const { createWritable } = require('wrote')
const makePromise = require('makepromise');

(async () => {
    // create a temp file and open a writable stream
    const ws = await createWritable()
    await closeWritable(ws)

    const { path: file } = ws

    console.log(file) // /var/folders/s0/tmp/T/wrote-69822.data

    // pass 3rd argument as the return value
    const resolvedFile = await makePromise(unlink, file, file)
    console.log(resolvedFile === file) // true
})()

More examples

Check test/spec/integration for the following tests:

• How to unlock a file with lockfile package
• How to write to a writable stream
• How to unlink a file with fs.unlink
• How to read stat with fs.stat
• How to catch errors after call fs.stat with non-existent file)

---

Licence: MIT

(c) Sobesednik-Media 2017