loban / devcon2017

The code for my talk at SoftExpo DevCon Bangladesh 2017

Please Wait, I Promise to Rid you of Callback Hell

This code was used during my talk at BASIS SoftExpo Developers Conference 2017. You can find the slides here, but the meat is in the code.

NodeJS development involves many tasks that 'block IO'. Since NodeJS is single threaded, things can easily get bogged down by the following.

1. Filesystem calls
2. Database calls
3. HTTP calls
4. Lengthy calculations

Hence, asynchronous APIs (with callbacks) were developed to prevent blocking.

However, asynchronous code with callbacks is often difficult to maintain. This can be mitigated by using the promise pattern, and then taking advantage of the async/await keywords in ES7.

1. Look at the synchronous example.
2. Look at the asynchronous example with callbacks.
3. Look at the asynchronous example improved with promises.
4. Look at the asynchronous example improved with async/await.

All examples do the same following tasks.

1. Load a json file, as fileContent.
2. Parse the fileContent into a jsonContent.
3. For each element of jsonContent, perform an http call, resulting in an httpContent array.
4. Store the httpContent in the database as dbContent.

There are potential errors in every step, and they are all handled.

To run the code, perform the following steps.

1. npm install
2. npm run build
3. node ./build/devcon2017-1.sync.js
4. node ./build/devcon2017-1.callback.js
5. node ./build/devcon2017-1.promise.js
6. node ./build/devcon2017-1.await.js