<script>

function in_array(stringToSearch, arrayToSearch) {

     for (s = 0; s < arrayToSearch.length; s++) {

      thisEntry = arrayToSearch[s].toString();

      if (thisEntry == stringToSearch) {

       return true;

      }

     }

     return false;

}

var arr = [1,2,3,4,5];

if(in_array(3,arr)){

    alert(1);

}else{

    alert(2);

}

</script>