Merge branch '25188-polyfill-es-symbol' into 'master'

Enable array spread and destructuring through recommended Babel polyfills

Closes #25188 and #24922

See merge request !10120

app/assets/javascripts/commons/polyfills.js

 // ECMAScript polyfills
 import 'core-js/fn/array/find';
+import 'core-js/fn/array/from';
 import 'core-js/fn/object/assign';
 import 'core-js/fn/promise';
 import 'core-js/fn/string/code-point-at';
 import 'core-js/fn/string/from-code-point';
+import 'core-js/fn/symbol';
 // Browser polyfills
 import './polyfills/custom_event';

app/assets/javascripts/diff.js

@@ -33,11 +33,7 @@ class Diff {
   handleClickUnfold(e) {
     const $target = $(e.target);
-    // current babel config relies on iterators implementation, so we cannot simply do:
-    // const [oldLineNumber, newLineNumber] = this.lineNumbers($target.parent());
-    const ref = this.lineNumbers($target.parent());
-    const oldLineNumber = ref[0];
-    const newLineNumber = ref[1];
+    const [oldLineNumber, newLineNumber] = this.lineNumbers($target.parent());
     const offset = newLineNumber - oldLineNumber;
     const bottom = $target.hasClass('js-unfold-bottom');
     let since;
@@ -105,10 +101,11 @@ class Diff {
   }
   lineNumbers(line) {
-    if (!line.children().length) {
+    const children = line.find('.diff-line-num').toArray();
+    if (children.length !== 2) {
       return [0, 0];
     }
-    return line.find('.diff-line-num').map((i, elm) => parseInt($(elm).data('linenumber'), 10));
+    return children.map(elm => parseInt($(elm).data('linenumber'), 10) || 0);
   }
   highlightSelectedLine() {

changelogs/unreleased/25188-polyfill-es-symbol.yml

+---
+title: Add ECMAScript polyfills for Symbol and Array.find
+merge_request: 10120
+author: