[Deff]

var arr = [1, 2, 1, 10, 5, 3, 4, 40, 50],
bound = '\n\n===@@@==\n\n',
tststr = bound + arr.join(bound+bound) + bound,
out=[];
 for (var i = 0; i < arr.length; i++) {
     if(tststr.split(bound +arr[i] + bound).length <3)out.push(arr[i])
 }
alert(out)