End Callback Hell using Async and Await

Use of async, await, and Promise in Node.js v7 mark an end to Callback Hell in Javascript. This also works in a Web Browser if your code is transpiled using libraries like Babel.js or Typescript. If you're not sure what a callback is, watch this video.

Turn Callback Hell...

http.get('https://api.github.com/repos/nodejs/node', function(response) {
  console.log(response)
  http.get('https://api.github.com/repos/nodejs/http2', function(response) {
    console.log(response)
    http.get('https://api.github.com/repos/nodejs/docker-node', function(response) {
      console.log(response)
    })
  })
})

Into synchronous-looking yet non-blocking Heaven ..

var response = await http.get('https://api.github.com/repos/nodejs/node')
console.log(response)
var response = await http.get('https://api.github.com/repos/nodejs/http2')
console.log(response)
var response = await http.get('https://api.github.com/repos/nodejs/docker-node')
console.log(response)

Read the annotated code examples

The files you'll be interested in reading are located in the following locations in this repository.

.
├── basic-example
│   └── index.js
├── build-async-enabled-functions
|   └── index.js
└── advanced-usage-ftw
    └── src
        ├── error-handling.js
        └── index.js

Run the examples

Prerequisites

You can run two of the examples with Git and Node.js Installed on your system, but if you use Docker you can run the third advanced example and also not have to install Node 7 on your computer.

• Node.js 7 (http://nodejs.org/)
• Git (https://git-scm.com/).
• Docker (https://www.docker.com/community-edition)

Run using Node 7 installed on your computer

# Get the examples.
git clone [email protected]:rjsteinert/end-callback-hell-using-async-and-await.git
cd end-callback-hell-using-async-and-await

# Run the basic example.
cd basic-example
npm install
node index.js
cd ..

# Run the example showing how to build functions of your own that can be used with async.
cd build-async-able-functions 
npm install
node index.js
cd ...

Run using Docker

These examples require you to either have Node 7 installed on your computer or alternatively run them with Docker so you don't need to mess up your system. Only the advanced usage example will work if you are running Docker.

To run each of the examples with Docker, cd into their respective folders and run docker-compose up --build.

# Get the examples.
git clone [email protected]:rjsteinert/end-callback-hell-using-async-and-await.git
cd end-callback-hell-using-async-and-await

# Run the basic example.
cd basic-example
docker-compose up --build
cd ..

# Run the example showing how to build functions of your own that can be used with async.
cd build-async-able-functions 
docker-compose up --build
cd ...

# Run the advanced-usage example.
cd advanced-usage
docker-compose up --build
cd ...

You should play with these examples! Break them. Improve them. Make a pull request.

Why not just use Promises?

Promises are the formalization of callback culture into a language feature. This formalization makes async and await possible.

What about using then to chain together functions that return Promises?

Functions are great when you give them input, you get some output. In that case they are discreet pieces of functionality. When their input is scattered all over different parts of an object, it’s tough to track down their requirements and make sure certain things run in the correct order. It's the classic separation of concerns problem and why globals are discouraged.