CCM-10140: message content preview links should open in new tab (#510)

Author: alexnuttall

frontend/src/__tests__/utils/markdownit/__snapshots__/index.test.tsx.snap

@@ -12,7 +12,7 @@ exports[`renderEmailMarkdown should only process email markdown rules 1`] = `
 <li>ordered list item 1</li>
 <li>ordered list item 2</li>
 </ol>
-<p><a href="https://www.nhs.uk/example">Read more</a></p>
+<p><a href="https://www.nhs.uk/example" target="_blank" rel="noopener noreferrer">Read more</a></p>
 <p>https://www.nhs.uk/example</p>
 <p>Before page break</p>
 <hr>
@@ -38,7 +38,7 @@ exports[`renderNHSAppMarkdown should only process nhs app markdown rules 1`] = `
 <li>ordered list item 1</li>
 <li>ordered list item 2</li>
 </ol>
-<p><a href="https://www.nhs.uk/example">Read more</a></p>
+<p><a href="https://www.nhs.uk/example" target="_blank" rel="noopener noreferrer">Read more</a></p>
 <p>https://www.nhs.uk/example</p>
 <p>Before page break
 ***

frontend/src/utils/markdownit/index.ts

@@ -4,6 +4,13 @@ import { lineBreak } from './plugins/line-break';
 export class MarkdownItWrapper extends MarkdownIt {
   constructor() {
     super('zero');
+
+    // rendered links should open in a new tab
+    this.renderer.rules.link_open = (tokens, idx) => {
+      const href = tokens[idx].attrGet('href');
+
+      return `<a href="${href}" target="_blank" rel="noopener noreferrer">`;
+    };
   }
 
   /**