Promising to node-rest-client

I’m currently in love with Promises. Somehow, only now I get the main concept behind that and the benefits. Mainly, because most of the documentation is a bit too detailed about that.

Let me sum it up for you:

If you’re developing asynchronous Javascript (which you should be, when you’re actually developing Javascript!), most of the time you’re passing callback functions to asynchronous functions:

function async(callback) {
  // do something
  if (there_is_an_error) {
    callback(error);
  } else {
    callback(null, { something: 'return' }); // everything's fine
  }
}

function callAsync() {
  async(
    (error) => {
      if (error) {
        // handle error
      } else {
        // keep on working
      }
    }
  );
}

This gets very ugly if you’re chaining multiple callbacks after another. There are helpers for that – for example the wonderful Async.js (and that’s the first choice when it comes to asynchronous calls in loops), but it still gets ugly.

Promises, however, allow you to chain callbacks and handling errors in a much more cleaner way:

function async() {
  return new Promise(function (fulfill, reject) {
    // do something
    if (there_is_an_error) {
      reject(error);
    } else {
      fulfill({ something: 'return' }); // Everything's fine
    }
  });
}

function callAsync() {
  async()
    .catch(
      (error) => {
        // handle error
      }
    )
    .then(
      () => {
        // keep on working
      }
    );
}

Well, this example is not that good to show you the benefits, but think about five callbacks in a row. If you’re using a column limit in your code conventions, you’ll be effectively writing on the right border of your screen. Not with Promises.

To wrap this post up, I have a present for all folks using node-rest-client. I’ve made a Promise wrapper around it using Bluebird and I’ve called it node-rest-client-promise. Just grab it using „npm install node-rest-client-promise –save“ instead of node-rest-client and use it like this:

var nodeRestClient = require('node-rest-client-promise');

var client = nodeRestClient.client({
  // node-rest-client.Client-options 
});

client.getPromise(
  'https://www.google.de'
).catch(
  (error) => {
    // there was an error
  }
).then(
  () => {
    // everything's great.
  }
);

Have fun.

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