Fallback to previous, more approximative hashtag RE on older browsers (#14513)

Fixes #14511

app/javascript/mastodon/features/compose/containers/warning_container.js

@@ -5,10 +5,12 @@ import PropTypes from 'prop-types';
 import { FormattedMessage } from 'react-intl';
 import { me } from '../../../initial_state';
 
-const HASHTAG_SEPARATORS = "_\\u00b7\\u200c";
-const ALPHA = '\\p{L}\\p{M}';
-const WORD = '\\p{L}\\p{M}\\p{N}\\p{Pc}';
-const APPROX_HASHTAG_RE = new RegExp(
+const buildHashtagRE = () => {
+  try {
+    const HASHTAG_SEPARATORS = "_\\u00b7\\u200c";
+    const ALPHA = '\\p{L}\\p{M}';
+    const WORD = '\\p{L}\\p{M}\\p{N}\\p{Pc}';
+    return new RegExp(
       '(?:^|[^\\/\\)\\w])#((' +
       '[' + WORD + '_]' +
       '[' + WORD + HASHTAG_SEPARATORS + ']*' +
@@ -20,7 +22,13 @@ const APPROX_HASHTAG_RE = new RegExp(
       '[' + ALPHA + ']' +
       '[' + WORD + '_]*' +
       '))', 'iu'
-);
+    );
+  } catch {
+    return /(?:^|[^\/\)\w])#(\w*[a-zA-Z·]\w*)/i;
+  }
+};
+
+const APPROX_HASHTAG_RE = buildHashtagRE();
 
 const mapStateToProps = state => ({
   needsLockWarning: state.getIn(['compose', 'privacy']) === 'private' && !state.getIn(['accounts', me, 'locked']),