use const and arrow function instead of function

src/client/js/components/RevisionCompare.jsx

@@ -33,7 +33,7 @@ function encodeSpaces(str) {
 
 const PageCompare = (props) => {
 
-  const toggleDropdown = () => {
+  function toggleDropdown() {
     setDropdownOpen(!dropdownOpen);
   }
 

src/client/js/components/RevisionCompare/RevisionIdForm.jsx

@@ -12,7 +12,7 @@ const RevisionIdForm = (props) => {
   /**
    * create an Option array for AsyncSelect from the revision list
    */
-  function revisionOptions() {
+  const revisionOptions = () => {
     const { revisions } = props.pageHistoryContainer.state;
     const timeFormat = 'yyyy/MM/dd HH:mm:ss';
 
@@ -25,7 +25,7 @@ const RevisionIdForm = (props) => {
    * render a revision selector
    * @param {label} label text of inputbox
    */
-  function renderRevisionSelector(label) {
+  const renderRevisionSelector = (label) => {
     if (['FromRev', 'ToRev'].indexOf(label) === -1) {
       return <></>;
     }