Javascript - typeof etc

Whats so complicated in providing methods to find a type of a variable? Reading on Stackoverflow makes you wish javascript dies sooner than later:

if (value instanceof Array) {
  alert('value is Array!');
} else {
  alert('Not an array');
}

Why on earth does typeof arrayvariable return object ?!?

Okay - lets use JQuerys $.isArray(variable).

While at it - array.truncate(index) would also be nice. Yes i know you can do it with splice or slice but both return a new object. I simply want to truncate the array without caring about the additional indexes.