#jslang Meetup - Errors

in Event 4 minutes read

In our offices we have a monthly meetup, which is all about JavaScript language features, we call it “JavaScript The Language” (see twitter #jslang). We pick one language feature and by writing tests for each piece of the feature we step by step explore the feature in depth.

The plan

The plan for the meetup was to:

  1. Collect items that we want to learn about JavaScript Errors
  2. Write tests to learn, verify and describe some Error properties.

How we ran the meetup

We organized the meetup on meetup.com.


We started by introducing each other shortly. Then we did 1. and collected items. We came up with this:

  • TypeError, RangeError, …
  • async await
  • Promise handling
  • properties and methods,
  • assert
  • catching
  • extend Error
  • Error() as a function
  • stacktrace

We started by trying out how to cause a TypeError or RangeError. We fiddled around a bit and figured out that reading up on MDN helps us to understand better what we need to do to cause errors. Of course accessing [][0] the first elements of an empty array does not trigger a RangeError, as we assumed first. But in the end we found out how to trigger RangeError and TypeError (see the tests) and so on. The funny thing was that now, we looked much more closely on what error our tests throw and we learned a lot just from failing tests. Of course we also read into the spec a little bit.

Along the way we also dug into undefined, arrays, JSON.stringify and others. We covered some of the things that we had listed at the beginning of the session, but as usual we didn’t cover it all.

My personal impression was that it was a good evening. I was afraid that we would not have enough things to explore around errors and that we would sit around being bored or finding artificial tasks, but that was not the case by far. Instead we learned quite some things about errors and touched on some other topics too. That is what I like about those meetups, you never know how it goes and the people who are there drive it, which makes it unique every time. Thanks to the participants for a great evening.

Planning the next Meetup

At the end of every meetup we collect a set of language features which we vote on to determine the next meetup’s topic. This time we collected some topics while writing our code during the meetup, this is the list we came up with:

  • Array
  • Symbol
  • Proxy
  • async errors
  • SharedArrayBuffers and Atomics

As you can see here the next meetup will be about Proxies.