perf: Remove markdown serialize from editor render path (#3567)

* perf: Remove markdown serialize from editor render path

* fix: Simplify heading equality check

* perf: Add cache for slugified headings

* tsc

shared/editor/lib/headingToSlug.ts

@@ -2,16 +2,25 @@ import { escape } from "lodash";
 import { Node } from "prosemirror-model";
 import slugify from "slugify";
 
+const cache = new Map<string, string>();
+
 // Slugify, escape, and remove periods from headings so that they are
 // compatible with both url hashes AND dom ID's (querySelector does not like
 // ID's that begin with a number or a period, for example).
 function safeSlugify(text: string) {
-  return `h-${escape(
+  if (cache.has(text)) {
+    return cache.get(text) as string;
+  }
+
+  const slug = `h-${escape(
     slugify(text, {
       remove: /[!"#$%&'\.()*+,\/:;<=>?@\[\]\\^_`{|}~]/g,
       lower: true,
     })
   )}`;
+
+  cache.set(text, slug);
+  return slug;
 }
 
 // calculates a unique slug for this heading based on it's text and position