fixed title extraction to exclude latex code, but include rendered latex (#946)

Signed-off-by: Philip Molares <philip.molares@udo.edu>

cypress/integration/documentTitle.spec.ts

@@ -95,11 +95,21 @@ describe('Document Title', () => {
     })
 
     it('markdown syntax removed third', () => {
-      cy.get('a')
-        .get('@codeinput')
+      cy.get('@codeinput')
         .fill(`# ${title} _asd_`)
       cy.title()
         .should('eq', `${title} asd - HedgeDoc @ ${branding.name}`)
     })
+
+    it('katex code looks right', () => {
+      cy.get('@codeinput')
+        .fill(`# $\\alpha$-foo`)
+      cy.get('.markdown-body > h1')
+        .should('contain', 'α')
+      cy.get('@codeinput')
+        .type('\n\ntest\n')
+      cy.title()
+        .should('eq', `α-foo - HedgeDoc @ ${branding.name}`)
+    })
   })
 })

src/components/markdown-renderer/hooks/use-extract-first-headline.ts

@@ -9,6 +9,11 @@ import React, { useCallback, useEffect } from 'react'
 export const useExtractFirstHeadline = (documentElement: React.RefObject<HTMLDivElement>, content: string, onFirstHeadingChange?: (firstHeading: string | undefined) => void): void => {
   const extractInnerText = useCallback((node: ChildNode): string => {
     let innerText = ''
+
+    if ((node as HTMLElement).classList?.contains("katex-mathml")) {
+      return ''
+    }
+
     if (node.childNodes && node.childNodes.length > 0) {
       node.childNodes.forEach((child) => { innerText += extractInnerText(child) })
     } else if (node.nodeName === 'IMG') {