From 79bbfde4444f366d6132b3c87b52d1ee44f43aef Mon Sep 17 00:00:00 2001
From: Eoghan Murray <eoghan@getthere.ie>
Date: Tue, 12 Jan 2021 16:55:11 +0000
Subject: [PATCH] Discovered that the common case of mouse movement or
 scrolling happening during `takeFullSnapshot` was causing mutations to be
 immediately emitted, contrary to the goal of
 https://github.com/rrweb-io/rrweb/pull/385

---
 src/record/index.ts          |  9 ++-------
 src/record/mutation.ts       | 19 ++++++++++++++++---
 typings/record/mutation.d.ts |  2 ++
 3 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/src/record/index.ts b/src/record/index.ts
index 164d1e1933..11ead12958 100644
--- a/src/record/index.ts
+++ b/src/record/index.ts
@@ -116,7 +116,6 @@ function record<T = eventWithTime>(
     ) {
       // we've got a user initiated event so first we need to apply
       // all DOM changes that have been buffering during paused state
-      mutationBuffer.emit();
       mutationBuffer.unfreeze();
     }
 
@@ -153,8 +152,7 @@ function record<T = eventWithTime>(
       isCheckout,
     );
 
-    let wasFrozen = mutationBuffer.isFrozen();
-    mutationBuffer.freeze();  // don't allow any mirror modifications during snapshotting
+    mutationBuffer.lock();  // don't allow any mirror modifications during snapshotting
     const [node, idNodeMap] = snapshot(
       tdoc,
       blockClass,
@@ -193,10 +191,7 @@ function record<T = eventWithTime>(
         },
       }),
     );
-    if (!wasFrozen) {
-      mutationBuffer.emit();  // emit anything queued up now
-      mutationBuffer.unfreeze();
-    }
+    mutationBuffer.unlock();  // generate & emit any mutations that happened during snapshotting, as can now apply against the newly built mirror
   }
 
   try {
diff --git a/src/record/mutation.ts b/src/record/mutation.ts
index 89b6ee8781..e4ca92b77c 100644
--- a/src/record/mutation.ts
+++ b/src/record/mutation.ts
@@ -170,20 +170,33 @@ export default class MutationBuffer {
 
   public unfreeze() {
     this.frozen = false;
+    this.emit();
   }
 
   public isFrozen() {
     return this.frozen;
   }
 
+  public lock() {
+    this.locked = true;
+  }
+
+  public unlock() {
+    this.locked = false;
+    this.emit();
+  }
+
   public processMutations = (mutations: mutationRecord[]) => {
     mutations.forEach(this.processMutation);
-    if (!this.frozen) {
-      this.emit();
-    }
+    this.emit();
   };
 
   public emit = () => {
+
+    if (this.frozen || this.locked) {
+      return;
+    }
+
     // delay any modification of the mirror until this function
     // so that the mirror for takeFullSnapshot doesn't get mutated while it's event is being processed
 
diff --git a/typings/record/mutation.d.ts b/typings/record/mutation.d.ts
index f57d7b8e54..97e18cf179 100644
--- a/typings/record/mutation.d.ts
+++ b/typings/record/mutation.d.ts
@@ -19,6 +19,8 @@ export default class MutationBuffer {
     freeze(): void;
     unfreeze(): void;
     isFrozen(): boolean;
+    lock(): void;
+    unlock(): void;
     processMutations: (mutations: mutationRecord[]) => void;
     emit: () => void;
     private processMutation;