js six strange literals

check.js

function check(v) {
    var out = {}
    out.value = v

    if (v) {
        out.ifCheck = true
    } else {
        out.ifCheck = false
    }

    out.trueCheck = (v == true)
    out.falseCheck = (v == false)

    out.strictTrueCheck = (v === true)
    out.strictFalseCheck = (v === false)

    console.log(out);
}

check(NaN)
check(undefined)
check(0)
check(false)
check('')
check(null)

/** Output



{ value: NaN,
  ifCheck: false,
  trueCheck: false,
  falseCheck: false,
  strictTrueCheck: false,
  strictFalseCheck: false }
{ value: undefined,
  ifCheck: false,
  trueCheck: false,
  falseCheck: false,
  strictTrueCheck: false,
  strictFalseCheck: false }
{ value: 0,
  ifCheck: false,
  trueCheck: false,
  falseCheck: true,       <<< notice this ouput here (0 == false) if true, however (0 === false) is false
  strictTrueCheck: false,
  strictFalseCheck: false }
{ value: false,
  ifCheck: false,
  trueCheck: false,
  falseCheck: true,
  strictTrueCheck: false,
  strictFalseCheck: true }
{ value: '',
  ifCheck: false,
  trueCheck: false,
  falseCheck: true,          <<< notice this ouput here ('' == false) if true, however ('' === false) is false
  strictTrueCheck: false,
  strictFalseCheck: false }
{ value: null,
  ifCheck: false,
  trueCheck: false,
  falseCheck: false,
  strictTrueCheck: false,
  strictFalseCheck: false }



*/