var newStr = '';

var array = [1,2,3,4,1,2,6,7];

for (var i in array)
	{
		for (var j in array)
			{
				if (array[i] != array[j])
					{
						newStr += array[i];
					}
				
			}
	}

alert(newStr);

var mass1 = [1, 2, 3, 2, 4, 5, 6, 7, 8];
var mass2 = [45,1, 3, 3, 1, 12, 12, 45];
function prov(mass){
 for (var i = 0; i < mass.length; i++){
  for (var j = i; j < mass.length; j++){
   if (i != j){
    if (mass[i] == mass[j]){
     alert("Нумерация с нуля - mass[" + i + "] == mass[" + j + "]\n" + mass[i] + " == " + mass[j]);
    }
   }
  }
 }
}
prov(mass1);
prov(mass2);

var newStr = '';
 var array = [1,1,3,4,1,1,6,7];
 var str = array.join(",");

var Sin=str;
function Replacer(str, p1, offset, s) {
  var reg = '/'+p1+',?/g';
  var reg2 = '/'+p1+',?/';
  var s2;
  var s2=Sin.replace(eval(reg2),'');
  var s3=s2.replace(eval(reg),'')
  if(s3!=s2)Sin=s3;
  return p1 +',';
} 
 str = str.replace(/(\d*?),/g,Replacer).replace(/^.*?$/g,Sin).split(",");
alert(str);

<script type="text/javascript">
var newStr = '';
 var array = [111,1,111,2,33,3,44,5,33,44,6,77,77];
 var str = array.join(",")+",";

var Sin=str;
function Replacer(str, p1, offset, s) {
  var reg = '/'+p1+',?/g';
  var reg2 = '/'+p1+',?/';
  var s2;
  var s2=Sin.replace(eval(reg2),'');
  var s3=s2.replace(eval(reg),'')
  if(s3!=s2)Sin=s3;
  return p1 +',';
} 
str = str.replace(/(\d*?),/g,Replacer).replace(/^.*?$/g,Sin);
str=str.substring(0,str.length-1).split(",");
alert(str);

</script>

var arr = [1,2,3,4,1,2,6,7];

var tmp_arr = new Array();

	for (i = 0; i < arr.length; i++) 
    {
		if (tmp_arr.indexOf(arr[i]) == "-1") 
        {
			tmp_arr.push(arr[i]);
		}
	}
      

alert(tmp_arr);