Question

I have a function that returns a value that can be true if the condition is met and false if not, but the function can also return a string message in case of an error.

I need to differentiate between the true/false boolean values under normal conditions without mistaking the string value for either one. My strategy is to use a parseBoolean() function that will return a true Boolean-typed true/false value when passed a boolean input, but a “falsy” value that isn’t a Boolean-typed false when passed a string.

Example

function validate(kkk)
{
  //... some check that validates 
  return true;
  //... some check that doesn't validate
  return false;
  //... failure - return explanation
  return 'Error Message jjjjjjjj';
}

function usingit(data)
{
  if(parseBoolean(validate(data)) != false)
  {
    /// the value is Boolean true
  }
  else
  {
    if(parseBoolean(validate(data)) === false)
    {
      /// the value is Boolean false
    }
    else
    {
      /// the value is false but not of a Boolean type 
      /// so we will display it as the error message text.
    }
  }
}

…but I haven’t figured out how to create a parseBoolean() function that behaves this way. Any ideas?

Answer 1

According to this:

@Esailija Why no sense? If it is true return a true, if it is false
return false, if it is ‘somestring’ also return false. Get it? –
Registered User 31 secs ago

You want

function parseBoolean(value) {
    return typeof value == "boolean" ? value : false;
}

But this obviously won’t pass the test of doom.

---

This code passes all your tests:

function parseBoolean(bool) {
    return typeof bool == "boolean" ? bool : 0;
}

if( parseBoolean('anystring') == false ) {
    alert("");
}

if( parseBoolean('anystring') !== false ) {
    alert("");
}

if( parseBoolean(true) ) {
    alert('');
}

if( !parseBoolean(false) ) {
    alert('');
}