[Demath]

Тупо перебором

function Arrays(A,B)
{
    var m = A.length, n = B.length;
  
    for (var i = 0; i < m; i++)
     { for (var j = 0; j < n; j++)
        { if (B[j] === A[i][0]) B[j] = A[i][1]; }
     }
 
    return B;
}

var arrA = [['1','a'],['2','b'],['3','c'],['4','d']],
    arrB = ['1','4','2','8','1','6','5','2','4'];
alert( Arrays(arrA,arrB) );