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Tony Mottaz

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Writing code for both computers and humans

October 15, 2023

One day, I was reading some source code from the Adobe Spectrum
library when I saw this JavaScript ternary expression:

isNaN(defaultValue) ? NaN : defaultValue;

This made me pause for a moment. The logician in me was confused why
such an expression was necessary--this ternary is equivalent to just
using the value of defaultValue. If defaultValue were NaN then we get
back NaN anyway.

But then I realized that this code lead me through that thought
process in the first place because it was written this way. If you
think about it, this code expresses a lot of information:

  * defaultValue is going to be a number
  * It is possible that the value is NaN
  * The author who implemented this code considered and handled this
    possibility
  * A NaN value is explicitly forwarded through

Now consider the alternative. What if the author left this as just
defaultValue? If you saw that, your spidey-sense might start
tingling, "This is a number--did they consider the NaN case?" To
answer this question, you need to start looking around for clues.
Maybe they left a comment explaining this, but more often you will
need to read the surrounding code to find out. Or worse, run some
tests. Or worse worse, write new tests. Or worse worse worse, run the
app and manually test!

This ternary is much better. This is expert-level programming. This
is how to write code with empathy for other programmers.

I tip my cap to @snowystinger (who wrote this expression, and best as
I can tell) and the rest of the Spectrum team.

Tony Mottaz

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