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 || [];

What does it means and/or what’s it for, and how do you use it?

Thank you.

Answer 1

The logical operators in JavaScript actually evaluate to one of the two objects. When you use a || b it evaluates to b if a is false, or to a if a is true. Thus a || [] will be a if a is any value that is true, or [] if a is any value that is false.

It’s much more obvious to use if (!a) { a = [] };