JavaScript check if variable exists (is defined/initialized)

Question

Which method of checking if a variable has been initialized is better/correct? (Assuming the variable could hold anything (string, int, object, function, etc.))

Answer 1

Short way to test a variable is not declared (not undefined) is

if (typeof variable === "undefined") {
  ...
}

I found it useful for detecting script running outside a browser (not having declared window variable).