What is this in [removed] “var var1 = var1 || []”

Question

I just want to increase my core javascript knowledge.

Sometimes I see this statement but I don\'t know what it does:

var var1 = var1 || [];

Answer 1

The || operator evaluates the first of its operands that is "truthy".

[] is an empty array. ([ "Hi!" ] is an array of one string)

Therefore, the expression x || [] evaluates to x if it's "truthy" or an empty array if it isn't.

This allows the var1 parameter to be optional.