What does “var FOO = FOO || {}” (assign a variable or an empty object to that variable) mean in Javascript?

Question

Looking at an online source code I came across this at the top of several source files.

var FOO = FOO || {};
FOO.Bar = …;

But I have no ide

Answer 1

If there is no value in AEROTWIST or it is null or undefined the value assigned to the new AEROTWIST will be {} (a blank object)