From faab271d1e4ca91bd7bcf64dae5c3ef9e7e86988 Mon Sep 17 00:00:00 2001
From: James Garbutt <43081j@users.noreply.github.com>
Date: Thu, 18 Apr 2024 00:03:12 +0100
Subject: [PATCH] feat(labs/ssr): use RegExp.exec to escape HTML

Switches from using `replace(pattern, fn)` to using the `exec` method of
a `RegExp` instead.
---
 packages/labs/ssr/src/lib/util/escape-html.ts | 63 ++++++++++++++-----
 1 file changed, 49 insertions(+), 14 deletions(-)

diff --git a/packages/labs/ssr/src/lib/util/escape-html.ts b/packages/labs/ssr/src/lib/util/escape-html.ts
index d0d66edd62..d4a4e56ab6 100644
--- a/packages/labs/ssr/src/lib/util/escape-html.ts
+++ b/packages/labs/ssr/src/lib/util/escape-html.ts
@@ -4,22 +4,57 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-const replacements = {
-  '&': '&amp;',
-  '<': '&lt;',
-  '>': '&gt;',
-  '"': '&quot;',
-  // Note &apos; was not defined in the HTML4 spec, and is not supported by very
-  // old browsers like IE8, so a codepoint entity is used instead.
-  "'": '&#39;',
-};
+const escapePattern = /[&<>"']/g;
 
 /**
  * Replaces characters which have special meaning in HTML (&<>"') with escaped
  * HTML entities ("&amp;", "&lt;", etc.).
  */
-export const escapeHtml = (str: string) =>
-  str.replace(
-    /[&<>"']/g,
-    (char) => replacements[char as keyof typeof replacements]
-  );
+export const escapeHtml = (str: string) => {
+  let match = escapePattern.exec(str);
+
+  if (!match) {
+    return str;
+  }
+
+  let escapeStr;
+  let html = '';
+  let lastIndex = 0;
+
+  while (match) {
+    switch (str.charCodeAt(match.index)) {
+      // Character: "
+      case 34:
+        escapeStr = '&quot;';
+        break;
+      // Character: &
+      case 38:
+        escapeStr = '&amp;';
+        break;
+      // Character: '
+      // Note &apos; was not defined in the HTML4 spec, and is not supported by
+      // very old browsers like IE8, so a codepoint entity is used instead.
+      case 39:
+        escapeStr = '&#39;';
+        break;
+      // Character: <
+      case 60:
+        escapeStr = '&lt;';
+        break;
+      // Character: >
+      case 62:
+        escapeStr = '&gt;';
+        break;
+    }
+
+    html += str.substring(lastIndex, match.index) + escapeStr;
+    lastIndex = match.index + 1;
+    match = escapePattern.exec(str);
+  }
+
+  escapePattern.lastIndex = 0;
+
+  return lastIndex !== str.length - 1
+    ? html + str.substring(lastIndex, str.length)
+    : html;
+};