A function without a return statement (or one that ends its execution without hitting one) will return undefined
.
And if you use the unary negation operator twice on an undefined
value, you will get false
.
You are not seeing anything on the console because Firebug doesn’t prints the result of an expression when it’s undefined (just try typing undefined;
at the console, and you will see nothing).
However if you call the console.log
function directly, and you will be able to see it:
function foo(){}
console.log(foo()); // will show 'undefined'