yz-yu 6de74d7bca close #280. Improve the performance of the DOM mutation observer. (#284)
This issue was originally reported in #280 but may also relate
to #167 and other potential performance issues in the recording.

In #206 I implemented the new mutation observer which will defer
the serialization of DOM, which helps us to have a consistent DOM
order for the replay.

In this implementation, we use an array to represent the `addQueue`.
Whenever we need to consume the queue, we will iterate it to make
sure there is no dead loop, and then shift the first item to see
whether it can be serialized at the new timing.

But this implementation may be very slow when there are a lot of newly
added DOM since it will do an O(n^2) iteration.

For example, if we have three newly added DOM `n1`, `n2`, `n3`,
the iteration looks like this:
```
[n1, n2, n3]
	n1 -> n2 -> n3, consume n3
[n1, n2]
	n1 -> n2, consume n2
[n1]
	n1, consume n1
```
We should have a better performance if te iteration looks like this:
```
[n1, n2, n3]
	n3, consume n3
[n1, n2]
	n2, consume n2
[n1]
	n1, consume n1
```

Simply reverse the mutation payload does not work, because it does
not always as same as the DOM order.

So in this patch, we replace the `addQueue` with a double linked list,
which can:
1. represent the DOM order in its data structure
2. has an O(1) time complexity when looking up the sibling of a list item
3. has an O(1) time complexity when removing a list item
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rrweb

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rrweb refers to 'record and replay the web', which is a tool for recording and replaying users' interactions on the web.

Currently, rrweb has already solved many difficult problems in recording and replaying, but the data structure may still be changed before the release of Version 1.0. So please be cautious to use rrweb in the production environment.

Guide

📚 Read the rrweb guide here. 📚

Project Structure

rrweb is mainly composed of 3 parts:

  • rrweb-snapshot, including both snapshot and rebuilding features. The snapshot is used to convert the DOM and its state into a serializable data structure with a unique identifier; the rebuilding feature is to rebuild the snapshot into corresponding DOM.
  • rrweb, including two functions, record and replay. The record function is used to record all the mutations in the DOM; the replay is to replay the recorded mutations one by one according to the corresponding timestamp.
  • rrweb-player, is a player UI for rrweb, providing GUI-based functions like pause, fast-forward, drag and drop to play at any time.

Roadmap

  • rrweb
    • handle cross-domain request errors
    • record in web worker
    • implement transmission data compression
    • verify recording in mobile browser
  • rrweb-player
    • implement efficient progress bar drag and drop control
    • add full screen mode
  • extensions
    • hijack the console API and record corresponding events
    • hijack Ajax/fetch API and record request events
    • use TraceKit to log exception events

Internal Design

Contribute Guide

Since we want the record and replay sides to share a strongly typed data structure, rrweb is developed with typescript which provides stronger type support.

Typescript handbook

  1. Fork the rrweb component repository you want to patch.
  2. Run npm install to install required dependencies.
  3. Patch the code and pass all the tests.
  4. Push the code and create a pull request.

In addition to adding integration tests and unit tests, rrweb also provides a REPL testing tool.

Using the REPL tool

Who's using rrweb

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