[Dilettante_Pro]

Подстрока в строке abcdeahopwunshslge

var str = 'abcdeahopwunshslge',
      limit,
      maxSS = '',
      j,
      indx,
      arr = [];
for(var i = 0; i < str.length; i++) {
     arr[i] = '';
      j       = i ;
      limit = str.length;
   while(j < limit) {
      arr[i] += str[j];
      indx = str.indexOf(str[j], j + 1);
      if(indx >= 0  && limit > indx ) { limit = indx;}
       j++;
    }
}
for (var i = 0; i < arr.length; i++) {
  if (maxSS.length < arr[i].length) { maxSS = arr[i];}
}
alert(maxSS);