Checking if a variable is either true or false

Question

In JavaScript I have a variable initialized with undefined. Now I'd like to check if it is either true or false.

Is there a statement more elegant than the following?

if (isValid === true || isValid === false) {
  // do something
}

Answer 1

How about checking if it is not undefined?

• If it is neither true, nor false it has to be undefined.
• So if it is not undefined, it is set and therefore either true or false.

if (isValid !== undefined) {
   // do something
}