Map and find duplicates in 2 arrays

findDupesInArray.js

// Arrays
var x = ["7","?","X","X","Q", "?"];
var y = ["?","X","Z","Q", "?", "?"]; 

var find_dupes = function (array1, array2) {
    
    /* Map Arrays, make uppercase if neccessary  
    var xx = array1.map(function(x){ return x.toUpperCase() })
    var yy = array2.map(function(x){ return x.toUpperCase() }) */

    // Sort xx against yy
    var map = array1.filter(function(val) {
      return array2.indexOf(val) != -1;
    });
    // return duplicates between arrays
    return JSON.stringify(map);
}

// Print Function
console.log(find_dupes(x,y));