check-dups.js

var known = [ 1, 6, 3, 9, 4 ];
var presented = [ 2, 5, 7, 4, 9, 4 ];

function done(missing, extraneous) {
  console.log('Missing:', missing);
  console.log('Extraneous:', extraneous);
}

check(known, presented, done);

function check(known, presented, done) {
  var stuff = {};

  function count(v) {
    var k = stuff[v];
    stuff[v] = k ? k + 1 : 1;
  }

  known.forEach(count);

  var common = [];
  var extraneous = [];
  presented.forEach(function (p) {
    if (stuff[p]) {
      if (!--stuff[p]) { common.push(p); }
    } else {
      extraneous.push(p);
    }
  });

  done(common, extraneous);
}