Armin Ronacher's Thoughts and Writings

Stop Being Cute and Clever

written on Monday, December 9, 2013

The last few days I spent a bit of my spare time on making a world time scheduler. Some of you might recognize the concept from another website. The idea was quite simple: build a clone of worldtime buddy and explore working with third party AngularJS directives and a few JavaScript libraries and try to reuse as much as possible.

It was not a fun experience. I have not raged so much about working with something in a really long time and that says something, because I'm quite quick at voicing my unhappiness (I'm so sorry for my Twitter followers).

I'm using JavaScript quite regularly on my own, but I very rarely need to deal with other people's code. Normally I pretty much stick to jQuery, underscore and maybe AngularJS and I stay focused on the browser or command line utilities. This time around though, I went all-in and used various libraries.

For this project I obviously used jQuery which is impossible to avoid (and why would you) but also AngularJS with a bunch of UI components (angular-ui and some bindings to jQuery UI). For timezone handling I used moment.js with moment-timezone.

Let me preface this in that I really don't want to criticise anyone's individual code here. More than that, if someone would look at my own JavaScript code it would not be any better. If anything it's worse, because I did not spend much time on it and I'm not very experienced with JavaScript.

However I do see a worrying trend of absolutely appalling code quality in JavaScript libraries (at least the selection of the ones I was using) and I started to do some thinking on why that is.

There are so many problems I have with JavaScript libraries and all of them are pretty much a result of how the language works and that nobody seems to care. Not that you could not write better code, but it seems like everybody gravitates towards falling into the same traps.

The reason I started actively looking into other people's JavaScript code was that my naive approach of sending 3MB of city names into the typeahead.js autocomplete library resulted in a really sluggish UI. Now obviously a clever person would not send that much into an autocomplete field. A better plan would be to filter the data on the server first, but it turns out that it wasn't the loading that was slow, but the filtering of the data. That made no sense to me, because even if the system did a linear search through 26.000 cities it should not have been this slow.


So the UI was slow — obviously it should be my fault of sending so many records. Interestingly though my performance degraded upon usage of the typeahead widget. In very peculiar ways even. To give you an idea of how crazy it, this was my reproduction case which I started out with:

  1. Search for San Francisco by typing "san". Takes ~200ms.
  2. Search for San Francisco by typing "fran". Takes ~200ms.
  3. Search for San Francisco by typing "san fran". Takes a second.
  4. Search for San Francisco by typing "san" again. Takes a second.

What's going on there? How does the search corrupt by finding more than one item once?

The first thing I did was using Firefox' new profiler to see where all the time is wasted. Quite quickly I found a whole bunch of stuff in typeahead that was just overly weird.

The slowness was relatively quickly found: an epic misuse of data structures and a weird algorithm. The whole way of how the library finds matches is pretty bizarre and includes such amazing things as going over a list of strings and then checking for each of those strings if it's contained within any of the other lists including the original list itself. When that first list has 6000 items and for each of those you do a linear search if it's indeed in the list this can indeed get pretty slow.

But mistakes happen and especially if you only test with small data sets you will not notice that. Me sending thousands of cities and timezones into the little thing was too much. Also not everybody writes search functions every day, so I don't blame anyone for that.

But because I had to debug this thing I found some of the most bizarre code I had the pleasure to read. Upon further investigation, it seems to be hardly a thing unique to typeahead.

Based on that I'm now pretty convinced now that JavaScript is the Wild West of software development. Primarily because it rivals 2003 PHP code in terms of code quality, but it seems fewer people care because it runs on the client instead of server. You don't have to pay for your slowly running JavaScript code.

“Clever” Code

The first pain point is people being cute and clever with JavaScript. And that makes me reviewing code and hunting for bugs ridiculously paranoid. Even if you know the idioms applied you will still not be sure if the side effects are intentional or if someone made a mistake.

To give you an example of such a weird idom, I want to show you some code from typeahead.js as it exists in the library, just reindented to make it look nicer:

_transformDatum: function(datum) {
    var value = utils.isString(datum) ? datum : datum[this.valueKey],
        tokens = datum.tokens || utils.tokenizeText(value), item = {
        value: value,
        tokens: tokens
    if (utils.isString(datum)) {
        item.datum = {};
        item.datum[this.valueKey] = datum;
    } else {
        item.datum = datum;
    item.tokens = utils.filter(item.tokens, function(token) {
        return !utils.isBlankString(token);
    item.tokens =, function(token) {
        return token.toLowerCase();
    return item;

This is just one function, but it's one that stuck with me for a wide range of reasons. What the function does is converting a datum object into an item. What's a datum? Well here it starts. It seems like the library author at one point re-decided his approach. It must have started out with accepting a string and then wrapping it in an object that has a value attribute (which is the string) and a token array which are the individual tokens. Then however it got messy and now the return value of that function is a wrapper around a datum object (or string) that has a slightly different interface. It copies a bunch of the input data over, but then it just renames some attributes. Assuming the input value is an object and not a string in this form:

    "value": "San Francisco",
    "tokens": ["san", "francisco"],
    "extra": {}

Then a transformation to this happens:

    "value": "San Francisco",
    "tokens": ["san", "francisco"],
    "datum": {
        "value": "San Francisco",
        "tokens": ["san", "francisco"],
        "extra": {}

I can totally see why the code ends up doing what it does, but from looking at a completely different piece of code first it became very confusing as of why my datum object became a slightly different datum object containing basically the same information. Worse: it uses double the memory because through the array operations it makes copies of the tokens. Looking around a bit it turns out that I could just send the correctly formatted datum objects in and cut down memory consumption by 10MB.

The reason though why I want to point out that code, is that it's quite idiomatic JavaScript code and that's frustrating. It's fuzzy and it's weird, lacks type information and is too clever.

It just sends objects around. You can't ask the datum: are you a datum. It's just an object. Given how similar the input data looked I expected the return value to be the same object, but it was not. Looking more into the implementation though it turned out that you could send a whole bunch of different types in — and it would still have worked, just done something else entirely and blown up much, much later. It's impressive how much bad input data you can send in and JavaScript will still somehow come up with results.

But not only does it lack type information, that code also tries to be really clever with using a mix of operator abuse and functional programming. I can't tell you how paranoid I am about this style of JavaScript nowadays given how weird the map functions works. Not many languages manages to implement map in a way that ["1", "2", "3"].map(parseInt) would result in [1, NaN, NaN].

Reasoning about JavaScript code is hard.

This however is not the extent of it. The abuse of language and operators is widespread. A bit further down this amazing piece of code can be found:

_processData: function(data) {
    var that = this, itemHash = {}, adjacencyList = {};
    utils.each(data, function(i, datum) {
        var item = that._transformDatum(datum), id = utils.getUniqueId(item.value);
        itemHash[id] = item;
        utils.each(item.tokens, function(i, token) {
            var character = token.charAt(0), adjacency =
                adjacencyList[character] || (adjacencyList[character] = [ id ]);
            !~utils.indexOf(adjacency, id) && adjacency.push(id);
    return {
        itemHash: itemHash,
        adjacencyList: adjacencyList

To fill in the reader: utils.indexOf is a linear search in an array and utils.getUniqueId returns an ever increasing integer as an actual integer.

Obviously the writer of this code knew about hash tables having an O(1) complexity, otherwise why would that person put that string into the hashmap. Yet a few lines of code later it does a linear search first before placing the item in the list. When throwing 100,000 tokens at this code, it gets really slow, trust me.

Also I would like to point out this loop:

utils.each(item.tokens, function(i, token) {
    var character = token.charAt(0), adjacency =
        adjacencyList[character] || (adjacencyList[character] = [ id ]);
    !~utils.indexOf(adjacency, id) && adjacency.push(id);

I'm pretty sure the author was very proud. For a start why is it written like this? Is !~utils.indexOf(...) && really a good replacement over if (utils.indexOf(...) >= 0)? Let alone the fact that the hashmap with the adjacency lists is called adjacencyList ... Or that the list is initialized with the ID of the string and then immediately a linear search is performed over that list to find the item again. Or that the entry in the hashmap is created by checking for the boolean-ness of the list and then using the or operator to invoke an assignment expression to place a list in the hashmap.

Another common hack I see is to use the unary plus operator (which in any other programming language is the most pointless operator ever since it's a noop) to convert a string into an integer. +value is pretty much the same as parseInt(value, 10). This is a ridiculous pattern and I wish it would not exist.

So I have this theory that this whole crazy business with operators is coming from Ruby. But in Ruby it made sense as there were only two objects that are false: false and nil. Everything else is true. Ruby's whole language is based on that concept too. In JavaScript many objects are false and then sometimes not.

For instance the empty string "" is false. Except when it's an object then it's true. Strings get promoted to objects by accident sometimes. For instance jQuery's each function passes the current value of the iterator as this. But because this cannot point to primitives like numbers and strings, the object needs to get promoted to a boxed string object. All the sudden it behaves different in some situations:

> !'';
> !new String('');
> '' == new String('');

Being cute with operators makes sense in ruby, but it makes no sense at all in JavaScript. It's dangerous. Not because I don't trust the developer to test his code and know what he's doing, but because later on someone else will have to look at the code and he will no longer know if the behavior was intentional or not.

To use the ~ operator to check the return value of an indexOf function that returns -1 for a missing match is just crazy business. And please don't come with the argument that it's faster.

We're Doing it Live!

Questionable use of operators and fuzzy typing is one thing, but the real killer is that people take the dynamic nature of JavaScript to the max. For me Python is already too much of a dynamic language, but at least Pythonistas are pretty reasonable with keeping runtime modification of classes and namespaces to a minimum. But no, not so in JavaScript, and especially not in the angular world.

Classes do not exist, in JavaScript you're doing objects and sometimes they might have prototypes. More often than not it's a big frack you to prototypes though and everybody just puts functions on objects. Sometimes also functions to functions for good measure. Weird object cloning is then par of the course except when it's not and state is just mutated left and right. The singleton is god.

You find an angular directive that's pretty good but does one thing differently than you wanted? There is a damn good chance it's monolithic though and the only way to modify is, is to attach a second directive at a higher priority that patches around in the scope of the other. I wouldn't even be unhappy if subclassing was a thing of the past, and composition was the way forward, but this monkeypatching business is just not my style.

The dynamic nature of everything makes code evolve very, very quickly into an unmanageable mess where nobody quite knows any more what something does any more.

It's not just the lack of classes and types though. The whole environment feels so much like a thing that is held together by duct tape on top of some layer of grease and paste.

Angular for instance uses this system of watching models and DOM for changes to automatically synchronize them. Except it's so damn slow at it, that people write weird workarounds to attempt to stop handlers from firing. This fuzzy logic quickly gets ridiculously confusing.

What is Immutability

The higher level a programming language goes, the more immutable things get. At least that was my feeling so far. Not so in JavaScript. APIs are littered with stateful concepts. Maybe it's misplaced performance thing but it gets annoying quickly. Some of the most annoying bugs I had to deal with in my scheduler app was the mutable nature of moment (date) objects. Instead of foo.add('minutes', 1) returning a new object, it modifies foo in place. It's not that I did not know about that, the API is quite clear about it. But unfortunately some code accidentally passed a reference out and it got modified.

Admittedly JavaScript should in theory be amazing for building APIs that use immutable objects considering you can freeze objects at will. This is something that Python unfortunately lacks. However at the same time Python has many more tools for making immutable objects interesting. For instance it supports operator overloading and has first class support for using immutable objects as hash keys. JavaScript has neither.

“Useful Magic”

I love angular, very much so. It's one of the sanest systems out there for UI design in JavaScript but the magic in it frightens me. It starts with the simple things where the library renames directives. If you make a directive called fooBar you will use it as foo-bar in the DOM. Why? I suppose consistency with the style DOM API which did something similar in the past. This makes looking for code really confusing because you might not quite know what the directive is called exactly. It also completely abolishes the idea of namespaces. If you have two directives with the same name in two different angular applications they will clash.

It does make the code more concise but also super confusing. It also subverts the rules of the language in parts. Dependency injection in angular happens by default through converting the JavaScript function back into a string (which yields the code) and then to use a regular expression to parse the function arguments. If you are new to Angular that makes no sense at all and even now I find the whole idea of doing it like this just inherently wrong. For a start, it subverts what JavaScript people have been doing for quite a while and that is treating local variables as basically anonymous. The name does not matter. This is something that minimizers have been taking advantage for ages. Obviously that does not fare well with Angular so it provides an alternative to explicitly declare dependencies.

What are Layers?

One of the biggest oddities coming from a Python environment to client side JavaScript is the apparent entire lack of abstractions. As an example of this, Angular provides a way to access the current URL's query parameters as dictionary. What however it does not provide is a way to parse arbitrary query strings. Why? Because the internal parsing function is hidden away behind layers of closures and someone did not think that would be useful.

And it's not just Angular, it's everywhere. JavaScript for instance lacks a function to properly escape HTML. But the DOM internally obviously needs to do this in places. So here is what I see people seriously suggesting as HTML escape function:

function escapeHTML(string) {
    var el = document.createElement('span');
    return el.innerHTML;

And it's not just parsing HTML that people do this way. Observe how to use the DOM for link parsing:

function getQueryString(url) {
    var el = document.createElement('a');
    el.href = url;

I find this insane, but it's absolutely everywhere.

In some ways I can understand that developers don't necessarily want to expose low-level functions but the end result is that users hack around in weird ways or duplicate the function for their own use. It's not uncommon to have half a dozen implementations of the same functionality in a larger JavaScript application.

“But it runs”

PHP got big because it just worked and it took no time to get started. A whole generation of developers started working with it and together that group of developers rediscovered years of prior experience in very painful ways. There was a group mentality where one person copied the next person's code and did not think much about how it works. I remember how plugin systems were just crazy talk and the common way for extensibility for PHP applications were mod files. Some misguided fool started that way and all the sudden everybody did it. I'm pretty sure that's exactly how we ended up with register globals everywhere, weird manual SQL escaping (if there was escaping at all), the whole concept of sanitizing input instead of proper escaping etc.

JavaScript is largely the same. While it's a different generation of developers and different problems, the whole mentality of copying together concepts found in one library into the next feels similar. Worse: because it's running in a sandbox and on people's computers nobody seems to give a thought about security at all. With the complete absence of escaping functions, HTML is concatenated with input strings left and right.

And unlike PHP performance does not matter because client side JavaScript “scales linearly with the number of users” running the application.

Angular is not inherently slow, but it's just so easy to make slow Angular directives and there are too many out there (and it's too easy to make your own slow ones). Since you don't pay for the CPU time it is not even a consideration.

The Future?

I'm not super pessimistic about JavaScript. It's definitely improving but I think it will go through the same phase of emancipation as PHP where people from other languages and environments are forced to work with it and slowly introduce sanity into the community. There will be a time after which the monkey patching of prototypes will stop, where stronger type systems will be introduced, people will start thinking about concurrency, where there will be a backlash over crazy meta programming and more.

Over the last few years you could see similar things happening in the Python community. A few years ago meta classes were the hot new thing and now that people write bigger and bigger applications some sanity has returned. When Django came out the developers had to defend the use of functions instead of classes. Now nobody talks much about that any more.

I just hope it will take the JavaScript community less time to adjust than others before them.

This entry was tagged javascript and thoughts