From 1ab5a281ab3cb3abc752c60006144362bf469713 Mon Sep 17 00:00:00 2001
From: Dawid Kisielewski <dawidpol1@gmail.com>
Date: Tue, 9 Jul 2024 09:31:35 +0200
Subject: [PATCH] =?UTF-8?q?=F0=9F=93=9D=20Add=20documentions=20about=20com?=
 =?UTF-8?q?pering=20old=20and=20new=20version=20of=20snapshot?=
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As per this discussion:
- https://github.com/share/sharedb/pull/667#discussion_r1654876315
---
 docs/middleware/op-submission.md | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/docs/middleware/op-submission.md b/docs/middleware/op-submission.md
index 737fd914..c09971ed 100644
--- a/docs/middleware/op-submission.md
+++ b/docs/middleware/op-submission.md
@@ -157,3 +157,26 @@ backend.use('apply', (request, next) => {
 
 {: .warn :}
 The `request.$fixup()` method may throw an error, which should be handled appropriately, usually by passing directly to the `next()` callback.
+
+## Comparing old snapshot version with new version
+
+Frequently, it becomes necessary to verify the changes made. This can be accomplished by leveraging two hooks, `apply` and `commit`, and creating a snapshot clone within the `apply` hook.
+
+```js
+// Alternatively use your favourite deep-clone library
+function deepClone(obj) {
+  return JSON.parse(JSON.stringify(obj));
+}
+
+backend.use('apply', (request, next) => {
+  request.snapshotBeforeApply = deepClone(request.snapshot);
+  next(error);
+});
+
+backend.use('commit', (request, next) => {
+  // Snapshot without ops and $fixupOps applied is now available as request.snapshotBeforeApply
+  // Snapshot with ops and $fixupOps applied is still available as request.snapshot
+  console.log(request.snapshotBeforeApply)
+  next(error);
+});
+```
\ No newline at end of file