JS 判断某个字符串是否存在与数组中

<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>