One of the common complains while developing with event loop platforms (Vert.x, Node.js, etc…) is that you will sonner or latter face callback hell.

Callback hell is a syntom of poorly organized code or the drawbacks of callback style programming where returns are not blocked until a response arrives from the callee.

Vert.x provided some tools to help fighting this issue:

  • executeBlocking (not really a solution since it just delegates to an good old thread pool)
  • RXified API’s
  • Completable Future API’s
  • Vert.x-Sync for the Java developers

Now if you’re doing JavaScript development then you can add another tool to the toolbelt. Armed with Webpack and Babel one can promisify the Vert.x API and use promisses. What is so amazing with this is that there are babel plugins that can now transforms async await calls to Promisses and this will then allow us to escape the callback hell.

Here is an example:

// get a reference to the web webclient class from java
const WebClient = Java.type('io.vertx.webclient.WebClient');

// in order to use await one needs to make a call from a async function, so we wrap our main code into
// and async function
(async function () {
  // error handling can be done with try catch
  try {
    let webClient = WebClient.create(vertx).get(80, "", "/");
    // since vertx API is callback style we need to convert that into a Promise style, either you do it manually
    // or use this helper that wraps a object and returns a proxy that adds a extra last parameter to all method
    // calls that handles the async result objects
    let response = await Promise.devertxify(webClient).send();
    // there was no threads involved in this code, the call was async and run on vert.x event loop
    // however you did not need to create callbacks and chain functions! hurray!!!
    console.log("Received response with status code: " + response.statusCode());
  } catch (e) {
    // oops! there was an error on the callback but now it is all managed as if it was blocking code,
    // just handle the exception in a try catch block!

How it works

All you need is enable the transformation in .babelrc:

  "presets": ["es2015"],
  "plugins": ["async-to-promises"]

A link to the full example is here.

Paulo Lopes

I'm Paulo and I've used my 10+ years of software development experience writing, rewriting, banging my head against the wall, editing and re-editing high-performance web application to make Vert.x an even more awesome framework.

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