Wednesday, August 19, 2009


Oddities of Boolean evaluation in JavaScript

I had some naive notions about how JavaScript evaluated certain Boolean expressions. For example, I assumed that code like
if (x) { ... }
would always evaluate like
if (x == true) { ... }
I was wrong. For example,
if ([]) { ... }
evaluates to true, but
if ([] == true) { ... }
evaluates to false.

I wrote the following test to help me identify other perilous JavaScript irregularities.
Read the squares as:
if (y)


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