Check if normalize is supported

Author: sy-records

docs/plugins.md

@@ -62,6 +62,12 @@ By default, the hyperlink on the current page is recognized and the content is s
 <script src="//cdn.jsdelivr.net/npm/docsify/lib/plugins/search.min.js"></script>
 ```
 
+The search ignores diacritical marks by default, but is not supported by IE. If you need support, please load this `ponyfill`
+
+```html
+<script src="//polyfill.io/v3/polyfill.min.js?features=String.prototype.normalize"></script>
+```
+
 ## Google Analytics
 
 Install the plugin and configure the track id.

src/plugins/search/search.js

@@ -132,7 +132,10 @@ export function genIndex(path, content = '', router, depth) {
 }
 
 export function ignoreDiacriticalMarks(keyword) {
-  return keyword.normalize('NFD').replace(/[\u0300-\u036f]/g, '');
+  if (keyword && keyword.normalize) {
+    return keyword.normalize('NFD').replace(/[\u0300-\u036f]/g, '');
+  }
+  return keyword;
 }
 
 /**