Stop Abusing the JavaScript Ternary Operator

http://karthikv.net/blog/javascript-ternary-operator

by karthikksv • 13 years ago

5 8 13 years ago

daleharvey• 13 years ago

Often a good reason to use not so pretty code is for performance reasons, you didnt mention checking up on that so it would probably be prudent to do so (micro optimisations are totally valid for hot paths in libraries like jquery and browser performance is often very unintuitive)

Also if I was going to write it 'cleaner', I would find something like http://pastie.org/7118990 cleaner.

(but in essence I agree)

karthikksv• 13 years ago

Do ternary operators really make much of a performance difference compared to if-else statements? I'd imagine they're not implemented much differently when it comes down to the instruction level (you still have the conditional branch). If they do make a difference, I'd hope the browser makes the optimization. Nevertheless, as you mention, this may not be the case.

marti221• 13 years ago

It's not about the actual number of operations the code compiles down to... it's about the number of bytes sent across the wire on initial page load. Among the most important elements of optimizing a webpage is minimizing the initial HTTP latency/download size. The jQuery core team is hyper-aware of all of these performance issues, and are doing everything possible to cut the gzipped/compressed size of their library. When you support a library that is literally run on the majority of the internet, these small improvements make a HUGE difference in the overall bandwidth consumption and load times of web applications.

I agree with you that use of the ternary operator, when not used properly, can obfuscate some code that could be simplified with if/else operators. But, jQuery has chosen to forgo readability for performance (and for good reason IMO).

gruseom2• 13 years ago

On the contrary. I prefer

  for (var i = 0; i < arr.length; i++) {
    arr[i] = foo(i) ? bar(i) : baz(i);
  }

  for (var index = 0; index < array.length; index++) {
    if (foo(index)) {
      array[index] = bar(index);
    } else {
      array[index] = baz(index);
    }
  }

in every way, including for readability.

The example is trivial but instructive. Each line in the second version is arguably more readable (in isolation) than its counterpart in the first, yet the verbose version as a whole imposes a longer time-to-comprehension on the reader — especially if you allow for the ability to grok idioms at a glance that one inevitably acquires after working with a given language or system for some time.

In my experience this argument becomes increasingly compelling as one applies it to more complex programs. What the naive notion of "readability" fails to account for is the compounding complexity tax of verbosity. It's a bit like analyzing the profitability of a trading system without considering transaction costs.

One more thing, with apologies for this being patronizing: an infatuation with an explicit spell-everything-out standard of readability seems to be a rite of passage on the path to programming maturity. I certainly went through it. I remember laughing uproariously at some of P.J. Plauger's (very tight and regular) library code years ago. I even remember shouting something like "if a programmer working for me ever wrote code like that, I'd fire them!" I literally did not know what I was talking about.

benaiah2• 13 years ago

He explicitly mentions that short ternary expressions like this are fine. My rule of thumb is that if it fits comfortably on one line, it's fine to use the ternary. (Of course, my real rule of thumb is to use CoffeeScript in the first place, but that's not always an option.)

gruseom2• 13 years ago

You're right and that's a fair point, but the argument still applies. The OP takes it as obvious that his rewritten jQuery snippet is better. In fact it's far from obvious, and learning the sense in which it's far from obvious is (in my experience) an important milestone, after which one stops arguing naively about readability and starts thinking more about the intelligibility of whole programs. If composed ternaries are an idiom that jQuery employs to do certain things compactly and repeatedly, that convention may well make it easier to understand jQuery. And that is what matters—not helicoptering into arbitrary bits of code.

In terms of lines of code—an imperfect metric but a useful one—his rewritten example is twice as long. That may seem like a small price to pay for an easier-to-understand snippet in isolation but if you start thinking about a complex system as a whole, and consider how complexity compounds as programs grow, that intuition changes considerably.

(I'm done being patronizing now.)

msoad• 13 years ago

CoffeeScript is not even close!

It can't even understand this code which is legit but horrible

    a = ()-> Math.random() * 1000 - 500
    b = ()-> Math.random() * 1000 - a()

    c = a == b ? a() < 0 ? a(b()) : b() : a(a())

http://coffeescript.org/#try:a%20%3D%20()-%3E%20Math.random(...

Stop Abusing the JavaScript Ternary Operator

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