check image accept only png,jpg,gif and Jpeg using javascript

<script language="javascript" type="text/javascript">

 function validate() {
      var result = false;
      var upfile = document.getElementById("FileUpload1").value;
      if (upfile != "") {
      var accept = "png,gif,jpg,jpeg".split(',');
      var getExtention = upfile.split('.');

 var extention = getExtention[getExtention.length - 1];
      for (i = 0; i < accept.length; i++) {
        if (accept[i] == extention) {
                result = true;
                break;
                        }
                    }

 if (!result) {
     alert(" Only Allowed here file extention are png,gif,jpg,jpeg");
                    }
                }
                else {
                  alert("please select image to Upload");
                }
                return result;
            }
        
</script>

 <asp:button id="btnUploadImage" onclick="btnUploadImage_Click" 
onclientclick="return validate();" runat="server" 

 text="Upload to DataBase">