[Dilettante_Pro]

function clearArrayFromUndefined(){
   var i = 0;
   do {
        if(array[i] === undefined) array.splice(i, 1);
        else i++;
    }   while (i < array.length);
}


var array = [];

array[0] = 0;
array[1] = 1;

array[3] = 3;

array[5] = 5;
array[8] = 8;
array[15] = 15;
array[20] = 20;
//array[50] = 50;

console.log(array);
clearArrayFromUndefined();
console.log(array);