First Class Citizen: JavaScript

Tue, May 12, 2015 9-minute read


Think of the last time you were given a project or a new website to build. The coding language for the server was not what you focused on. You likely thought more about how complex the site would be and what server side framework you would use to create the site.

Let’s say you worked through the feature list and landed on using Rails or Django as your server side web framework. Here are a few assumptions you made by choosing to have Python or Ruby as your core language (even if this was not a conscience choice):

  • Consistent and stable runtime
  • Manageable testing
  • Error handling
  • Built in logging

Why bring up these fairly standard features which exist in nearly every modern language? Because, most people seem to think JavaScript either does not have these features or people choose not use these features. In either case I’ll cover why JavaScript has all of these features and why we should rely on them instead of living in fear of them. I also plan to dispel what I believe is a commonly held myth: “Your JavaScript will fail.”

Hitting on that last point first, let’s start with what drives your thoughts when it comes to core language assumptions.

Why does your mindset matter?

If you live by the thought: “My JavaScript will fail” then it will fail. Think about it. If you wrote server side code under the assumption it will fail, you lack confidence in your application. Further if you lived under this thought you would probably not use the language or framework causing this much doubt in your applications. Do not misunderstand my point here. I am not saying that JavaScript can’t fail. I am saying that your mindset should be: “My JavaScript can fail”.

With the broader mind set of: “Code can fail” you will approach problems differently. – Notice I said code, that’s because this is how I think you should mentally approach all languages and frameworks you use in application development. – Instead of building for edge cases and having layers of fall back you can build the same as you do for the server. For instance if the server called another service you would not “progressively” enhance your interpretation of the service response. You assume you have some stability and reasonably handle failures. Maybe you return a 500 in those cases but give a reasonable message on what went wrong, or tell the user to try again. Similar approaches can be taken on the client

Instead of doing a complex fall back strategy for a feature you can (and should) implement the one that should always work and in the case of failure reasonably handle the failure. For example, when building a visualization you can use something like D3 or R2D3. If the visualization is unable to be built in the particular browser, don’t just fail or try to fall back to a bunch of different layers. Have a table be the one time fall back.

The difference between will fail and can fail: will fail mindset tries to build many layers of fall back (e.g. canvas, divs). This leads to more complicated code as well as less reliable code. A can fail mindset builds for the common successful case and reasonably handles failure. We need to handle errors on the client the same as we do the server. It’s not okay to gobble up errors and move on. Later we’ll see how you can gracefully handle errors and report on them.

I’m hoping you understand the difference between the two types of mindsets. Keep this core philosophy in mind as we move forward: “Code can fail”.

Consistent and stable runtime

In a world with many different browsers and various versions of those browsers it seems like we do not have consistent or stable runtimes. When it comes to Internet Explorer stability and consistency really do seem to be lacking. Please do not stop here though. Just because one browser is not completely reliable does not mean we do not have a consistent and stable runtime.

Thinking of desktop development, below is what I’ve seen as an example “support matrix”.


The parallel I draw to Ruby or Python here is when they are ran on different operating systems or interpreters. For the most part we do not have worry about the differences between operating systems. This is largely due to successful abstractions in the languages. I believe JavaScript has this same capability when paired with libraries. For instance you may use jQuery for a lot of your JavaScript code. This abstraction helps you achieve a consistent and stable environment.

Manageable testing

Nearly every language or framework comes with some decent work flows for testing. Usually all code that can be tested then gets tested. For instance if you have an ATM application where a person deposits money or withdraws money, you would test all parts of this work flow.

For some reason when it comes to the browser many developers think it’s okay to leave work flows untested that are impacted by JavaScript. Worse, because these work flows are often not tested changes may cause defects in the application later. Still growing negative, when JavaScript encounters errors it often results in the application not working.

It may sound like testing is hopeless in JavaScript. That is not the case there are plenty of ways to test JavaScript. In fact here are a list of frameworks that can help you out with testing (and a comparison):

With many tools available there is no excuse for not testing every part of an application that has end user impact. All of your JavaScript should be tested. If it’s not tested it shouldn’t exist.

Some will say that with closures (since JavaScript is heavily functional) that testing is really hard. Just because something is hard does not give you freedom to ignore it. Further, if the code is designed well testing usually isn’t an issue. A good sign of “code smell” is not being able to more easily create tests. This statement holds true to me for all code, not just JavaScript.

Error handling

Performance seems to be the first thing many people bring up when it comes to JavaScript error handling. I do not buy into this philosophy. Feel free to take a read of this programmer thread about the perceived issue. The real problem is if you’re using error handling as control flow. Don’t do that, you wouldn’t do it on the server so don’t do it in JavaScript. Exception cases are exceptional, therefore, they should not happen often. This means you need not worry about the performance impact because the errors are rare.

One point where people seem to think error handling doesn’t work in JavaScipt is in a setTimeout call. For example if you have this:

try {
    c = a + b;
  }, 100)
} catch (e) {
  alert("This will not be hit, ever!");

In Chrome you’ll see this error with the above code:

Uncaught ReferenceError: a is not defined

You may wonder why the error isn’t caught. I invite you to watch this great video about the event loop in JavaScript. Basically this is how JavaScript works. When code is sent to the event loop it is removed from the scope of this try catch. The code is made asynchronous by the setTimeout call. Therefore the try/catch no longer works because try/catch was a synchronous call.

There is actually a pretty easy way to handle this type of asynchronous call. Wrap the function passed to setTimeout in a try catch and you’ll be good. For example:

var realFunction = function () {
  c = a + b;

var handleErrors = function (func) {
  try {
  } catch (e) {
    alert("This line is hit, mischief managed!");

setTimeout(handleErrors(realFunction), 100);

I recommend this practice to anyone who wants to catch and handle errors. This gets back to a point before around hard-to-write tests. Error handling should also be as easy as it is in other languages. If the code is hard to handle, odds are it needs some refactoring. The code above can be used in a generic sort of wrapper to catch errors. Keep a look out, in the near feature I plan to help release a library to make this kind of error catching much easier. In fact, that same library plays a part in the next section of this post.

Built in logging

In most every language logging is built in. You make a call similar to:

  # something that breaks but is specific
except Exception as e:
  logger.error('Some specific message');

In JavaScript you do have access to console.log and the related levels of logging. If you are sitting there thinking that’s grossly inadequate compared to the power of server side logging, you are correct. Currently JavaScript lacks the ability to make it easy to aggregate logs.

Don’t throw console.log and friends out. They are very useful and give you the same power as other languages built in logging. The real issue is the lack of seeing all the logs across all of your users. When you have a 500 on your website you can see the number of times it occurs, who it impacts, and usually trace it to the line of code that caused the issue. This can all be done in production.

When it comes to getting a JavaScript error, a single log doesn’t really help you. The average user is not going to know how to get you the local client side logs. Further, most users won’t even realize what has gone wrong. A good number of users will usually refresh the page and hope for the best, or worse they will abandon their current pursuit and stop using the site.

Remember that library I mentioned above? The one that I plan to open source soon? Well, that library will make it very easy to get these JavaScript errors into one location for you to look at any time you want. The beauty of the library is how easy it is to track the errors.

I’ll finish by showing all that’s needed to catch all errors for a function that is used often.

var myUsedOftenFunction = function () {};;

That’s all you need. From then on if that function throws an error, in any browser, you’ll know about it.


When you develop code your mindset matters most. If you approach a problem assuming your tools won’t work, then you won’t solve the problem, and your tools won’t work. JavaScript is a powerful language that has many feature. Take advantage of these features and do not cripple yourself living in the world of “code will fail”.

Remember “code can fail” and you have a massive tool belt to handle these code failures. Embrace the power of JavaScript. Treat it like you do any other programming language. You only need to give JavaScript a chance. It can be one of your biggest assets when it comes to web development.