Question

If co.chkShowRSB is false, what is the expected result? I would expect it to be false, but is this the way it works? And why?

var test = chkShow:co.chkShowRSB || true;

Answer 1

Ok, so you got the picture by now x = false || true; assigns true. Why? It’s quite easy knowing the use of the short-circuit-operator is the same as doing:

x = (false ? false : true);

However, it’s mostly used to set default values for function arguments, so I’m guessing you’re assuming x to be assigned the second operand if the first is undefined. There is no way to filter out undefined values exclusively except for explicitly checking for them. You should then use:

x = val === undefined ? defaultVal : val;

Or, because undefined needn’t be undefined, and you want to be absolutely sure:

x = (function(val,undefined)//second argument will be the true undefined value
{
    return (val === undefined ? defaultVal : val);
})(val);//don't pass second argument