_classof.js

// getting tag from 19.1.3.6 Object.prototype.toString()
var cof = require('./_cof');
var TAG = require('./_wks')('toStringTag');
// ES3 wrong here
var ARG = cof(function () { return arguments; }()) == 'Arguments';

// fallback for IE11 Script Access Denied error
var tryGet = function (it, key) {
  try {
    return it[key];
  } catch (e) { /* empty */ }
};

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