Babbel Bytes

Insights from the Babbel engineering team

Babbel @Tech Startup JobsFair 2015 in Berlin

Barbara –

Babbel @Tech Startup JobsFair

Babbel’s Tech and HR teams will be at the Tech Startup JobsFair Berlin Spring 2015 looking for top talents! Babbel is a highly people-oriented company with a strong learning culture. At Babbel, you have the opportunity to work with some of the top talents in the industry, on a highly advanced technology stack that is constantly evolving to keep up with the cutting edge of new developments.

All this is only possible thanks to the team we have put together here at Babbel. Tech team members always participate in the recruitment process, and follow up with mentoring programs for new hires.

Babbel developers take part in great local events and international conferences. Maybe you will be representing us at the next one! But first, come and meet our team at the event, including Boris Diebold, VP Engineering, who will be there to give a quick introduction to the company and answer any questions you may have about working at Babbel.

The Tech Startup JobsFair Berlin is on May 27th 2015, you can sign up now on Eventbrite – and if you’re a top software engineer, we look forward to meeting you there! Check out also our Jobs at Babbel.

Babbel @Tech Startup JobsFair

How to create a radial progress bar with SVG

Jayasurian and Jon –

Radial progress

JS Bin

What is it for?

A while back we implemented a little countdown timer, which involved creating a radial progress bar. We ended up building a SVG radial timer, however we found that a lot of online resources were a bit complicated. In the end we built a straight forward simple radial progress bar using SVG, CSS and JS.

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The 2nd Babbel Hackday - our review


Hack days, hackathons or hackfests are done frequently in IT-companies to bring together engineers, designers and product owners in a playful spirit. The second Babbel Hackday took place on October 24th, 2014 at St. Oberholz – a typical Berlin-Mitte bar we thought…

2nd Babbel Hackday

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MicroXchg 2015 recap


Last week, a lot of Babbel developers attended MicroXchg, the Microservices Conference here in Berlin.

The conference itself was really well-organized. Like really, really well. The speakers were very good, the schedule was audience-friendly (lots of longish breaks to socialize, eat and drink), and the talks were balanced between enthusiastic and down-to-earth.

This post summarizes our impressions and the learnings we returned with.

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Functional Programming - A Gentle Introduction


Wikipedia defines Functional Programming as:

A programming paradigm that treats computation as the evaluation of mathematical functions.

If this sounds like Mathematical mumbo-jumbo that is completely removed of your day-to-day work as a Software Engineer, then you’re not alone. More than anything, Functional Programming is a way of thinking about building software in a perhaps very different paradigm than we’re normally used to. Let’s break down what are the core building blocks of a Functional Language and see how they can help us deliver better, more maintainable and robust software that you’ll actually have fun writing.

functional programming

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TechStartupJobs Fair Berlin 2014

Babbel Bytes

Babbel at Techstartup-Jobfair May 2014

We are ramping up our team of currently 30 engineers in all areas (see current job openings).

You can also visit us at TechStartupJobs Fair Berlin on 20.11.2014.

My 12 weeks in Babbel’s Backend Service Team


Omosola and Team

As my internship comes to a close (only two days left!), it seems like a great time to reflect on the past twelve weeks of my life here with Babbel.

I have to say that twelve weeks ago, I had literally no idea what to expect (and yes, I understand that’s the popular incorrect American use of “literally” :) I didn’t know all that much about the company. I just knew that I was ridiculously excited to return to Berlin for the summer.

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JavaScript Function call interception


Function call interception allows us to execute code before and after a function call. A use case might be formatting before and logging after a certain operation. A simple implementation in JavaScript could look like this:


var myObj = {
  property: 1,
  sendTo: function (endpoint) {
    console.log('sending ' + + ' to ' + endpoint);

function format () {
  console.log('formatting ' +;

function log () {
    console.log('logging ' +;

before(myObj, 'sendTo', format);
after(myObj, 'sendTo', log);


function before (object, method, fn) {
  var originalMethod = object[method];
  object[method] = function () {
    originalMethod.apply(object, arguments);

function after (object, method, fn) {
  var originalMethod = object[method];
  object[method] = function () {
    originalMethod.apply(object, arguments);;

This technique, also called function wrapping, is used by sinon.js to create spies, stubs and mocks.

Building external URLs for a Rails application


When referring to URLs there are valid reasons for avoiding hard-coded string manipulation in models, controllers or views. One reason is the DRY principle. Having a central representation of a resource eliminates the need to adjust all depending URLs when a change becomes necessary.

The Rails router generates helper methods for paths and URLs for exactly this reason. Suppose we define a route for a patients resource as follows.

get '/patients/:id', to: 'patients#show', as: 'patient'

Then, for a given Patient with id 17 initialized in the controller, we can call the following path or url helpers in a view.

patient_path(@patient)   # /patients/17

patient_url(@patient)    #

Using the Rails path and url helpers is a common best practice. However, there is no clear best practice for building external URLs, i.e. URLs not belonging to the application.

In this post we suggest using URI Templates with the Addressable gem for building external URLs and we outline an example implementation.

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Video Clip and Survey on the 1st Babbel Hackday


A few weeks ago, I wrote about the 1st Babbel Hackday. Meanwhile we have produced a video clip using the on-site recordings. Also the results of our survey are available. They are very encouraging. See the nice infographic below!

View “1st Babbel Hackday” on YouTube.

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Rails Decorators using the Draper gem

Babbel Bytes

You might have experienced this yourself: Over time, Rails models are getting fatter and fatter and the complexity of helper classes increases.

It is good practice to keep complicated logic away from your views. But dealing with a lot of helper methods is also tedious and adding view-related logic to the model is not an option either.

The Decorator design pattern helps to solve this problem.

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TechStartupJobs Fair Berlin 2014


We are ramping up our team of currently 30 engineers in all areas (see current job openings).

You can also visit us at TechStartupJobs Fair Berlin on 14.05.2014.

There are free tickets available for jobseekers - get them here.

The 1st Babbel Hackday


Friday, April 4th, we held the first Babbel Hackday. Starting at 10 a.m, more than 40 developers, designers, analysts and product managers gathered at Co-Up at the backyard of the Adalbertstraße in Berlin-Kreuzberg for a full day of hacking madness.

The complete staff of Babbel’s Product and Engineering departments and the BI team took part in the event. At Babbel Product, Engineering, and BI work closely together on various apps for web and mobile platforms. While our main goal for the Hackday was to bring people together through temporary teams for light-hearted, hackday-only projects, we also intended to provide some space for any ideas lying dormant in the existing teams. We also just wanted to have a fun day, and we were anticipating some great results.

First Babbel Hackday Logo

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up.front - Webdesign and Frontend Meetup

Babbel Bytes

On Tuesday, the up.front meetup about Webdesign and Frontend will take place at Co-up in Berlin.

Topics include

  • Changing Behavior with Design
  • Confessions of an Alien: Attracting Non-coding People to Your Open Source Project
  • A Video Game Revolution is Happening… In Your Browser

Also on Tuesday, the support for Windows XP will officially end! Watch the countdown here and come to Co-up to celebrate this.

Save the date!

Tuesday, April 8, 2014 7:00 PM at Co-up

Developing the Babbel Android App


Babbel’s mobile apps continue to be a huge success. After we shipped our new iOS7 apps, it was time to give the Babbel Android App a treat and turn it into a full-feature app. Babbel is striving to provide the same user experience across all devices. No user should ever be hindered in her/his learning activities by having to adapt to different user experiences on Android, iOS or the web.

Babbel Android App

Device images licensed by the Android Open Source Project under CC-BY 2.5. The aforesaid does not apply to the screenshots of the Babbel Android App.

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Reminder: Ruby User Group meetup on Thursday

Babbel Bytes

On Thursday, 6th March there will be the next meetup of RUG::B, the Ruby User Group of Berlin.

There will be talks about

  • It Takes a Village to Make a Programmer
  • Death to Cookies
  • Ruby Storm - Distributed work on a self-scaling system using RabbitMQ

Find out more at the events page

GitHub Service Hook for AWS OpsWorks


TL;DR: Trigger a deployment of an app in AWS OpsWorks via a GitHub service hook when pushing a branch to your repository.

There are use cases where you want to deploy something straightforward, just by pushing your changes to a git repository, e.g. an update of an internal tool or a typo in a blog post.

For web applications, Heroku has such a workflow. You configure a Heroku remote repository, push to its master branch, and Heroku’s after-push hook takes care to roll out the new version of your application.

For hosting of static pages (or simple blogs like this one), GitHub Pages provide the same approach. If you push the content of your page organized as Jekyll project to a special branch called gh-pages then GitHub Page will compile the templates and host the result.

We wanted to have the same comfort for AWS OpsWorks. Most of our web applications and internal tools are running on OpsWorks, and at least for the internal tools, the deployment through Capistrano or the AWS Console has been too cumbersome.

We’ve proposed a service hook to GitHub which can trigger an application deployment on OpsWorks. And GitHub has integrated it.

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Dynamically Built Regular Expressions


TL;DR: If you need to build dynamically regular expressions memoize them. Compiling them is expensive.

I don’t like memoizing methods, or caching in general. Obviously, caching adds more complexity to your source code and might lead to more errors, or even worse, errors which are harder to reproduce because they only happen due to a specific history. For memoized methods, you have to ensure that there are no other dependencies for the result than the passed arguments. Or that the result of a memoized method does not reference a larger object tree ending with a memory leak. There might be even more pitfalls.

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Welcome to the Babbel Tech Blog

Babbel Bytes

Hello World! Welcome to the Babbel Tech Blog.

From today on, we, the Babbel engineering team, would like to share our experiences about developing and maintaining the Babbel platform: The website, various mobile apps and the infrastructure behind it.

Some information about us and our infrastructure:

  • We are currently 25 FTE in the engineering department growing rapidly and about 12 FTE in product development.
  • For our web applications, we are developing in Ruby and Javascript (and CoffeeScript).
  • We are developing mobile applications for iOS, Android and Windows (Phone and 8), and thus, using Objective C, Java and C#.
  • Most of our web applications are Ruby on Rails applications, some special purpose applications like our tracker is written in node.js
  • The infrastructure running our web applications is hosted on AWS, mostly on OpsWorks, some an Elastic Beanstalk.