Build a Boolean Check Function — freeCodeCamp

Solution for the freeCodeCamp lab “Build a Boolean Check Function.”

Challenge

Write a function booWho that:

1. Receives one argument.
2. Returns true if the argument is a boolean primitive (true or false).
3. Returns false for any other value (numbers, strings, arrays, objects, NaN, etc.).

Solution

See booWho.js.

function booWho(bool) {
  return typeof bool === "boolean";
}

How it works: typeof returns the string "boolean" only for the two boolean primitives, true and false. For every other type, typeof returns something else ("number", "string", "object", etc.), so the function returns false.

Test Cases

Input	Output
booWho(true)	true
booWho(false)	true
booWho([1, 2, 3])	false
booWho([].slice)	false
booWho({ "a": 1 })	false
booWho(1)	false
booWho(NaN)	false
booWho("a")	false
booWho("true")	false
booWho("false")	false