$.classof.js 565 Bytes
// getting tag from 19.1.3.6 Object.prototype.toString()
var cof = require('./$.cof')
  , TAG = require('./$.wks')('toStringTag')
  // ES3 wrong here
  , ARG = cof(function(){ return arguments; }()) == 'Arguments';

module.exports = function(it){
  var O, T, B;
  return it === undefined ? 'Undefined' : it === null ? 'Null'
    // @@toStringTag case
    : typeof (T = (O = Object(it))[TAG]) == 'string' ? T
    // builtinTag case
    : ARG ? cof(O)
    // ES3 arguments fallback
    : (B = cof(O)) == 'Object' && typeof O.callee == 'function' ? 'Arguments' : B;
};