wait-for-me

Return a function you can await for (promisify), from a function which signature is (args..., err).

Why

Most async functions of nodejs framework have this signature (nodejs fs, or databases such mongo or NeDB).

When you start coding some async stuff without Promises (because the function does not handle it and just has a callback as argument), you end up with a lot of callbacks inside others callbacks, a lot of if to handle the arguments (err, result), a lot of repetitions, a lot of indentations, and the code is just ugly, let's face it.

Promisifying those async functions allows you to think more easily with the processes that's going on and generally to have a cleaner code, way more logic when you read it (you don't need to have to think about contexts embedded into others contexts, then what-if else etc.).

Just check the examples below if you're not sure that fits your needs.

Syntax

It returns a function that encapsule the given function into a Promise.

const read = waitForMe(fs.readFile);
const insert = waitForMe(db.insert, db); // context (`this`) is needed sometimes

then/catch

You can use it with with classic then/catch syntax, eg:

import waitForMe from 'wait-for-me';
const read = waitForMe(fs.readFile);
 
read('/etc/passwd')
  .then(data => sendEmail(data))
  .catch(err => console.error(`Couldn't access /etc/passwd: ${err.message}`))

async/await

Or you can use it with the async/await keywords (you need Babel for now to handle them), eg:

import fs from 'fs';
import waitForMe from 'wait-for-me';
const read = waitForMe(fs.readFile);
 
try {
  const data = await read('/etc/passwd')
  sendEmail(data);
} catch(err) {
  console.error(`Couldn't access passwd: ${err.message}`);
}

Generally, the async/await notation is cleaner, especially if you have several of them:

...
const get = waitForMe(request.get, request);
const tweet = waitForMe(client.post, client);
 
try {
  // get the content of an image
  // then post the image to twitter
  // then post a tweet using the image
 
  const result = await get({ url: src, encoding: null });
  const media = await tweet('media/upload', { media: result.body });
  const t = await tweet('statuses/update', { status: 'Yep', media_ids: media.media_id_string });
  console.log('Tweet OK!');
} catch(error) {
  console.error(error);
}

All those functions are async but it's like there are not!

Promise

The project does not include any polyfill for Promise. If you are using a plain nodejs process, you won't need it, it's handled natively.

Origin

I started a project with some callbacks hell, then wanted to promisify some functions because it was ugly. Few days before, I saw a conversation about this topic, involving @RReverser who suggests this approach.

I really liked it, very clean code. I just added the context option for me but all credits go to him.

You can find other projects promisifying function but I found them more complicated, doing more stuff, having polyfill or other thing I didn't want.

I just wanted to promisify some function I pock, in a nodejs process, that's it.