Replay fix for Firefox — add <head> and <body> separately (#1133)

eoghanmurray · YunFeng0817 · web-flow · commit c28ef5f658ab · 2023-02-22T16:45:29.000+11:00
* Firefox fix: Allow the &lt;head&gt; and &lt;body&gt; to be added in two stages so that (presumably) stylesheet rules are ready to be applied when the body appears

The css which triggered the bug was simply

{
  margin-left: 220px;
  transition: margin-left .448s;
}

* Add a test case which can only be appreciated if you record against this file://, save the events to a html file, and then open the file in Firefox (without this PR applied)

* Apply formatting changes

* Ensure we don't apply this branch when using rrdom, where it is not necessary

* Apply formatting changes

* Rewrite insertion in order to be compatible with rrdom

Also easier to understand

* Delete transition.html

* Create grumpy-ways-own.md

---------

Co-authored-by: Yun Feng &lt;yun.feng0817@gmail.com&gt;
diff --git a/.changeset/grumpy-ways-own.md b/.changeset/grumpy-ways-own.md
@@ -0,0 +1,7 @@
+---
+'rrweb-snapshot': patch
+---
+
+Fix: CSS transitions are incorrectly being applied upon rebuild in Firefox. Presumably FF doesn't finished parsing the styles in time, and applies e.g. a default margin:0 to elements which have a non-zero margin set in CSS, along with a transition on them.
+
+Related bug report to Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1816672​
diff --git a/packages/rrweb-snapshot/src/rebuild.ts b/packages/rrweb-snapshot/src/rebuild.ts
@@ -438,6 +438,28 @@ export function buildNodeWithSN(
 
       if (childN.isShadow && isElement(node) && node.shadowRoot) {
         node.shadowRoot.appendChild(childNode);
+      } else if (
+        n.type === NodeType.Document &&
+        childN.type == NodeType.Element
+      ) {
+        const htmlElement = childNode as HTMLElement;
+        let body: HTMLBodyElement | null = null;
+        htmlElement.childNodes.forEach((child) => {
+          if (child.nodeName === 'BODY') body = child as HTMLBodyElement;
+        });
+        if (body) {
+          // this branch solves a problem in Firefox where css transitions are incorrectly
+          // being applied upon rebuild.  Presumably FF doesn't finished parsing the styles
+          // in time, and applies e.g. a default margin:0 to elements which have a non-zero
+          // margin set in CSS, along with a transition on them
+          htmlElement.removeChild(body);
+          // append <head> and <style>s
+          node.appendChild(childNode);
+          // now append <body>
+          htmlElement.appendChild(body);
+        } else {
+          node.appendChild(childNode);
+        }
       } else {
         node.appendChild(childNode);
       }
