var fruits = ["test"];
for (var i=0;i<500;i++){
    fruits.push("test");
}
//
var Datalist = document.getElementById('Datalist');
var frag = document.createDocumentFragment();
for (var i in fruits) {
       if (fruits.hasOwnProperty(i)) {
            var option = document.createElement("OPTION");
          option.textContent = fruits[i];
          option.value = fruits[i];
          frag.appendChild(option);
        }
   }
 Datalist.appendChild(frag);