JavaScript

var arr = []; // You do *not* need to use new Array
var c = 0;

for (var i=0; i < oel.length; i++) {
  var e = 0;
  while (e < arrIns.length) {
    if (oel[i] != arrIns[e]) {
       arr[c] = oel[i];
       c++;
    }
    e++;
  } // while-loop

} // for-loop
oel.length = 0; // reset oel array length to zero, so that you can use the array again

if(oel[i] != arrIns[11])
    { oel[i]; }; // When i wrote document.write(oel[i] code in this line I can archive these numbers.

delete oel[i];

Quote:

that is exactly the last 3 weeks I wanted to get back remaining array of numbers. The number that is 49 - 18 = 31

// add this after the line } // while-loop
document.write(arr.toString()); 

// add this after the line } // while-loop
document.write(arr.toString());
//instead of arr[add++] method is better useful in this line.

var arrIns  = [ "1","21","24","28","42","48",
                "12","23","34","36","37","46",
                "3","18","19","25","44","45"  ];

var arrLot  = [];
var arr     = [];
var add     = 0;

for(var i=1; i<50; i++)
{
    arrLot[i] = i;
    if(arrLot[i] != arrIns[0])
    if(arrLot[i] != arrIns[1])
    if(arrLot[i] != arrIns[2])
    if(arrLot[i] != arrIns[3])
    if(arrLot[i] != arrIns[4])
    if(arrLot[i] != arrIns[5])
    if(arrLot[i] != arrIns[6])
    if(arrLot[i] != arrIns[7])
    if(arrLot[i] != arrIns[8])
    if(arrLot[i] != arrIns[9])
    if(arrLot[i] != arrIns[10])
    if(arrLot[i] != arrIns[11])
    if(arrLot[i] != arrIns[12])
    if(arrLot[i] != arrIns[13])
    if(arrLot[i] != arrIns[14])
    if(arrLot[i] != arrIns[15])
    if(arrLot[i] != arrIns[16])
    if(arrLot[i] != arrIns[17])
    if(arrLot[i] != arrIns[18])
    if(arrLot[i] != arrIns[19])
        { arr[add++] = arrLot[i];}
}

// create and initialise - array to keep track of any number taken
    var taken = new Array(49);
    for (var i=49; i>0; i--) taken[i]=false;

    var lucky = [];
    var z     = 0;

    do{
        var q = Math.round(31 * Math.random());
        if(!taken[arr[q]]) {
            lucky[z] = arr[q];
            taken[arr[q]] = true;
            document.write(lucky[z] + "  ");
            z++;
        }
    }while(z<6);

// **NEW** add leading zero to numbers < 10
function zeroAdjust(n) {
    var t = "0"+n;
    return t.substring(t.length-2,t.length);
}

// these also need leading zero if < 10
var arrIns  = [ "01","21","24","28","42","48",
                "12","23","34","36","37","46",
                "03","18","19","25","44","45"  ];

var allLucky = arrIns.toString();

var arrLot  = [];
var arr     = [];
var count   = 0;
var t;
for(var i=1; i<50; i++)
  {
    // force i to string then
    // compare i with all lucky numbers
    if (allLucky.indexOf(zeroAdjust(i)) == -1 ) {
      arr[count] = i; // add +"" 
      count++;
    }
  } // for-loop

document.write("length of arr[] ="+ count +"<br>");

//==========  EXAMPLE  ===============
// Save & Restore an array
var arrIns  = [ "01","21","24","28","42","48",
                "12","23","34","36","37","46",
                "03","18","19","25","44","45"  ];

var arr_to_csv   = arrIns.toString();
document.write(arr_to_csv);

var arr_from_csv = [];
var tmp = arr_to_csv.split(",");

for (var i=0; i < tmp.length; i++) {
    arr_from_csv[i] = parseInt( tmp[i]);
    document.write(arr_from_csv[i]);
}
//====================================

//==========  EXAMPLE  ===============
// arrIns array of 3 x 6 (not "strings")
var arrIns  = [ [ 1,21,24,28,42,48],
                [12,23,34,36,37,46],
                [ 3,18,19,25,44,45]
              ];

document.write("lucky numbers, one week at a time<br>");
for (var week=1; week < 4; week++) {
  document.write("week no: "+ week +"<br>");

  for (var i=0; i < 6; i++) {
     document.write(arrIns[week-1][i]);
  }
}
//==================================== 

<form>
    <select size=3 id=sel>
        <option>one</option>
	<option>two</option>
	<option>three</option>
    </select>
    <textarea name=debugga cols=40 rows=10></textarea>
</form>