String.prototype.getUnique = function(){

   var u = {}, a = [], arr=this.split('');

   for(var i = 0, l = arr.length; i < l; ++i){

      if(u.hasOwnProperty(arr[i])) {

         continue;

      }

      a.push(arr[i]);

      u[arr[i]] = 1;

   }

   return a.join('');

}

​

document.getElementById('btn').onclick = getUniqueChar;

​

function getUniqueChar() {

  document.getElementById('res').value = document.getElementById('str').value.getUnique();

}

​

setTimeout(getUniqueChar, 0);