fix eslint errors

app/assets/javascripts/copy_to_clipboard.js

-/* eslint-disable func-names, space-before-function-paren, one-var, no-var, one-var-declaration-per-line, prefer-template, quotes, no-unused-vars, prefer-arrow-callback, max-len */
-
 import Clipboard from 'clipboard';
 
-var genericError, genericSuccess, showTooltip;
+function showTooltip(target, title) {
+  const $target = $(target);
+  const originalTitle = $target.data('original-title');
+
+  if (!$target.data('hideTooltip')) {
+    $target
+      .attr('title', title)
+      .tooltip('fixTitle')
+      .tooltip('show')
+      .attr('title', originalTitle)
+      .tooltip('fixTitle');
+  }
+}
 
-genericSuccess = function(e) {
+function genericSuccess(e) {
   showTooltip(e.trigger, 'Copied');
   // Clear the selection and blur the trigger so it loses its border
   e.clearSelection();
-  return $(e.trigger).blur();
-};
+  $(e.trigger).blur();
+}
 
 // Safari doesn't support `execCommand`, so instead we inform the user to
 // copy manually.
 //
 // See http://clipboardjs.com/#browser-support
-genericError = function(e) {
-  var key;
+function genericError(e) {
+  let key;
   if (/Mac/i.test(navigator.userAgent)) {
     key = '⌘'; // Command
   } else {
     key = 'Ctrl';
   }
-  return showTooltip(e.trigger, "Press " + key + "-C to copy");
-};
-
-showTooltip = function(target, title) {
-  var $target = $(target);
-  var originalTitle = $target.data('original-title');
-
-  if (!$target.data('hideTooltip')) {
-    $target
-      .attr('title', 'Copied')
-      .tooltip('fixTitle')
-      .tooltip('show')
-      .attr('title', originalTitle)
-      .tooltip('fixTitle');
-  }
-};
+  showTooltip(e.trigger, `Press ${key}-C to copy`);
+}
 
-$(function() {
+$(() => {
   const clipboard = new Clipboard('[data-clipboard-target], [data-clipboard-text]');
   clipboard.on('success', genericSuccess);
   clipboard.on('error', genericError);
 
-  // This a workaround around ClipboardJS limitations to allow the context-specific copy/pasting of plain text or GFM.
-  // The Ruby `clipboard_button` helper sneaks a JSON hash with `text` and `gfm` keys into the `data-clipboard-text`
-  // attribute that ClipboardJS reads from.
-  // When ClipboardJS creates a new `textarea` (directly inside `body`, with a `readonly` attribute`), sets its value
-  // to the value of this data attribute, focusses on it, and finally programmatically issues the 'Copy' command,
-  // this code intercepts the copy command/event at the last minute to deconstruct this JSON hash and set the
-  // `text/plain` and `text/x-gfm` copy data types to the intended values.
-  $(document).on('copy', 'body > textarea[readonly]', function(e) {
+  /**
+   * This a workaround around ClipboardJS limitations to allow the context-specific copy/pasting
+   * of plain text or GFM. The Ruby `clipboard_button` helper sneaks a JSON hash with `text` and
+   * `gfm` keys into the `data-clipboard-text` attribute that ClipboardJS reads from.
+   * When ClipboardJS creates a new `textarea` (directly inside `body`, with a `readonly`
+   * attribute`), sets its value to the value of this data attribute, focusses on it, and finally
+   * programmatically issues the 'Copy' command, this code intercepts the copy command/event at
+   * the last minute to deconstruct this JSON hash and set the `text/plain` and `text/x-gfm` copy
+   * data types to the intended values.
+   */
+  $(document).on('copy', 'body > textarea[readonly]', (e) => {
     const clipboardData = e.originalEvent.clipboardData;
     if (!clipboardData) return;