Mark's Dev Blog

Presentations: How I Made Immer Twice as Fast: Performance Optimization in Practice

Thu, 26 Mar 2026 14:15:00 -0500

I've spent a lot of time debugging and doing performance optimization investigations throughout my career. It's second nature to me at this point, but a lot of developers have never really tried to investigate app performance.

In late 2025 I spent multiple months investigating and optimizing performance in the Immer immutable update library.

This talk covers how to approach performance investigation with a scientific approach mindset. It covers key investigation approach concepts, common perf profiling and visualization tools, and techniques to optimize code to run faster, and uses experiences from my Immer work as practical examples.

React Paris 2026

How I Made Immer Twice as Fast: slides

How I Made Immer Twice as Fast: video

Presentations: The State of React and the Community in 2025

Fri, 13 Jun 2025 14:15:00 -0500

I spend a lot of time reading (and participating in) discussions in the React community, across many different sites. Over the last few years I've seen an increasing amount of frustration and concerns from the community, questions about the motivations and intent behind React's development, and a growing disconnect between how the React team wants React to be used, and how the ecosystem is using React in practice.

I've put together this talk to explain and clarify what I'm seeing argued about. My goal is to answer questions, provide background context and explanation, highlight places where I'm seeing disconnects, and hopefully point out ways that things can be improved going forward.

React Summit 2025

I first did this talk at React Summit in June 2025. Here's the slides:

The State of React and the Community in 2025 - slides

I'll link the video of that talk as soon as it's available.

I also got to participate in a follow-up panel discussion on "The State of React". I'll link the video of that panel once it's available as well.

More Details: "The State of React and the Community" Post

Along with the talk, I've published an extensive post on "The State of React and the Community in 2025". This post goes into further details on the same topics, including more background and explanations of the pain points and concerns.

Hopefully this adds more depth to the limited amount of material I was able to cover in the talk!

Presentations: Maintaining a Library and a Community

Thu, 21 Nov 2024 21:00:00 -0500

The main thesis of this talk is that maintainers do a lot more than just write features and fix bugs, and that really most of what we do involves thinking about and interacting with the users of our library. That includes answering support questions, writing docs, thinking about how versioning and backwards compatibility will impact people, and a lot more.

Hopefully this proves useful to other maintainers, and peels back the curtain on what it's like to maintain a widely-used library.

React Summit US 2024

I first did this talk at React Summit US in November 2024:

Maintaining a Library and a Community - video

And here's the slides:

Maintaining a Library and a Community - slides

I also got to participate in a panel discussion on "The Future of React", with members of the React team and the community. This was a pretty good discussion:

The Future of React panel - video

NDC Oslo 2025

For NDC Oslo, I significantly expanded and updated the content and slides. Part of that is that I had an entire hour time slot instead of just 20 minutes, but also I thought of a lot more things to say :)

Maintaining a Library and a Community - slides

Video should be available online about a month after the conference, and I'll update this post once it's available.

https://www.youtube.com/live/42kUqbV3wIc?si=asXlCveJ_o660adX

React Advanced 2024: Designing Effective Documentation

Thu, 21 Nov 2024 20:00:00 -0500

My remote presentation for React Advanced 2024 was on "Designing Effective Documentation: Lessons Learned Writing the Redux Docs".

I've spent a lot of my time working on the Redux docs, and it is in fact how I got my start working on Redux!.

Hopefully this proves useful to other folks writing docs for tools and libraries.

Designing Effective Documentation - video

And here's the slides:

Designing Effective Documentation - slides

React Summit 2024: Why Use Redux Today?

Tue, 09 Jul 2024 23:00:00 -0500

I had the chance to speak at both React Connection Paris in April and React Summit Amsterdam in June, and at both conferences I gave a talk on "Why Use Redux Today?".

Both of those had the same core content, but I tweaked and updated the slides for React Summit.

Why Use Redux Today? - video

and the earlier livestream:

Why Use Redux Today? - livestream

And here's the slides:

Why Use Redux Today? - slides

React Summit US 2023: What's New in Redux Toolkit 2.0

Mon, 13 Nov 2023 23:00:00 -0500

I gave a lightning talk at React Summit US, and did a quick run-through of what's changing in RTK 2.0.

I've linked the livestream at the right timestamp for now, and will link the final video when it's live.

What's New in Redux Toolkit 2.0 - video

And here's the slides:

What's New in Redux Toolkit 2.0 - slides

(and totally unrelated to my talk, had the chance to lead a Carnival Parade of costumed characters as part of Kathleen McMahon's demonstration of "why you should never include a carousel in your design system!")

Kathleen McMahon: Carnival!!! - video

React Advanced 2023 - Building Better React DevTools with Replay Time Travel

Tue, 24 Oct 2023 10:00:00 -0500

I work at Replay.io, and I've spent all of this year building some incredibly advanced React debugging features that make use of our time-traveling backend API. The biggest one is our React DevTools integration. Early in 2023, I wrote a post for the Replay.io blog on How We Rebuilt React DevTools with Replay Routines, which recapped the initial working version. I've spent much of this year improving on that and building other related features.

At React Advanced, I got to share details on how the React DevTools work internally, and dive into how we extract React DevTools component tree data from recorded React apps using a combination of custom Chrome modifications and backend post-processing "routines" that leverage our time-travel API. Along the way, I showed off some crazy tricks like serializing JS functions as strings, sourcemapping original component names from production apps, and generating sourcemaps for React itself!

I also got to participate in a group panel discussion about Open Source, including questions about how we got involved and what it's like to "compete" with other OSS projects.

I've linked the livestream at the right timestamp for now, and will link the final video when it's live.

Building Better React DevTools with Replay Time Travel - video

And here's the slides:

Building Better React DevTools with Replay Time Travel - slides

and the OSS Panel video:

React Advanced Panel: Open Source - video

React Rally 2023 - A (Brief) Guide to React Rendering Behavior

Wed, 16 Aug 2023 14:00:00 -0500

My extensive post "A (Mostly) Complete Guide to React Rendering Behavior" is the most popular and widely appreciated post I've written. After the recent updates to cover React 18, it's now around 10,900 words long!

I recently had a chance to give a talk based on that post for React Advanced in 2022 and React Rally in 2023.

React Rally 2023

I'll link the video once it's available.

A (Brief) Guide to React Rendering Behavior - slides

A (Brief) Guide to React Rendering Behavior - livestream video

React Advanced 2022

A (Brief) Guide to React Rendering Behavior - video

And here's the slides:

A (Brief) Guide to React Rendering Behavior - slides

Presentations: Debugging JavaScript

Thu, 01 Jun 2023 10:00:00 -0500

In mid-2021 I had the chance to do a talk on "Debugging Software" for a meetup hosted by Mintbean.io. In 2022, I did an updated "Debugging JS" version of the talk for ThisDot Media's "JS Drops" video series.

I previously did a post on Debugging Tips, where I listed some quick tips for thinking about debugging, and recapped the stories of several interesting bugs I ran into and solved.

I later had a chance to present this talk at React Summit 2023 in Amsterdam.

This talk was based on that post, and covers:

Concepts and principles for thinking about debugging, as well as some additional tips
Specific techniques for debugging, including how to use both print logging and GUI debuggers effectively, as well strategies for debugging React, Redux, and JS
A quick example of using Replay to investigate bugs using time-travel debugging

The slides also include some "Scene of the crime"-themed versions of some of those debugging stories (not covered in the video due to time constraints).

Debugging JS - slides

Debugging JS - video ("JS Drops")

Presentations: 2022 Podcasts

Sun, 11 Dec 2022 12:00:00 -0500

I had the opportunity to talk on a number of different podcasts and interviews over the course of the year. I've gathered them here as a directory.

ThisDot / Tracy Lee: How to Contribute to Redux

Tracy Lee is a prolific podcaster, and her company ThisDot creates numerous shows related to the JS ecosystem. She had me on as part of a new "How to Contribute..." series, where I talked about ways to contribute to the Redux libraries.

https://www.youtube.com/watch?v=rPJmnxDX9lY

Kevin Ghadyani: Redux vs React Context

Kevin and I have done a couple long-form video discussions in the last couple years, and he's split those out into several separate videos.

This discussion was actually recorded in mid-2021, but just recently got published. We talked about the actual differences between Context and Redux, and why so many people get confused about the differences.

https://www.youtube.com/watch?v=1bIdaWVMFkc

PodRocket: Time-Travel Debugging with Replay (with Jason Laster)

I previously was a guest on the PodRocket podcast to discuss Redux topics. Shortly after I started working at Replay, they had me on again along with our CEO Jason Laster. We talked about the differences between Replay and "session recording" tools, the internals of how Replay works, and potential future use cases for time-travel debugging.

https://podrocket.logrocket.com/replay

Guild Community Tour: Mark Erikson

Taz Singh does a lot of interviews with folks in the JS community to help share their stories. He interviewed several folks at the Reactathon conference this year, and we had a chance to sit down and chat. We made a bunch of jokes about my Simpsons avatar, and talked about my early dev career, my time teaching in China, how I got involved in Redux, what prompted some of my blog posts, and the magic of time travel debugging with Replay.

https://beta.guild.host/presentations/episode-23-mark-erikson-bczaup

Peerlist: The Mindset of a Redux Maintainer

This was a meetup-type presentation of the "Modern Redux" talk I've done a couple times, but there were also some good questions asked afterwards.

https://www.youtube.com/watch?v=MbREkTZCcpc

20 Minute JS: Redux Toolkit and State Management in React

Fernando Doglio had me on to discuss some of the basics around "state management", why Redux became popular and then got a bad reputation, comparisons with other state libraries, and how we've modernized it with Redux Toolkit

https://podcast.20minjs.com/1952066/10665172-episode-12-redux-toolkit-and-state-management-in-react-with-mark-erikson

React Native Radio: A Redux Maintainer's Thoughts on Redux Toolkit vs Mobx-State-Tree

Earlier this year the React Native Radio podcast hosts did a show on Redux Toolkit vs Mobx-State-Tree. It was actually a very fair and balanced discussion, with a bit of a twist because host Jamon Holmgren is the maintainer of MST.

After listening to that episode, I had some thoughts on some of the topics they discussed, and reached out to Jamon. They brought me on for a follow-up episode where we dove into some of the points they'd brought up and I talked about why Redux is designed this way, including the purpose of immutability, pain points with selectors, and other tradeoffs. Really good discussion!

https://reactnativeradio.com/episodes/rnr-249-a-redux-maintainers-thoughts-on-rtk-vs-mst

Merged: Leading Tech Communities

Iddan Aaronsohn had me on the "Merged" podcast to discuss a number of topics around my involvement in the tech community. We talked about dealing with social media, sharing knowledge, working with open source, and more.

https://open.spotify.com/episode/67jTvkMB2vf7AYD5d8KSEs?si=DmNMOIuOSjaheIRI09-G_A&nd=1

Reactiflux Office Hours: Lenz Weber-Tronic and Mark Erikson

Carl Vitullo, one of the other admins in the Reactiflux Discord, held an "office hours" interview with myself and my RTK co-maintainer Lenz Weber-Tronic. We chatted about how we got involved with Redux, how users depend on implicit behavior of libraries, complexities of maintaining TypeScript libraries, the job searches we went through this year, and ways that people can get involved with open source.

https://open.spotify.com/episode/1xKYFWjPmtYwNY3DauQ2JB?si=LOhGBIrDQ5KI3034b6xvBQ

Presentations: Modern Redux with Redux Toolkit

Mon, 27 Jun 2022 20:00:00 -0500

I've frequently talked about why we created Redux Toolkit and what APIs it includes as part of my "State of Redux" talks and other similar presentations. I recently had the chance to talk at a couple of online meetups, and put together an updated and consolidated version of that material as a complete "Modern Redux with Redux Toolkit" presentation:

Modern Redux with Redux Toolkit - video

Modern Redux with Redux Toolkit - slides

Reactathon 2022: The Evolution of Redux Async Logic

Wed, 04 May 2022 12:00:00 -0500

I've spoken at Reactathon in past years, and this year I had the chance to give a pre-recorded talk. I also ended up giving the same talk live as well after filling in as a backup speaker.

My talk looked at why we use middleware for side effects in Redux, the major libraries (thunks, sagas, observables), why we've recommended thunks, introduces RTK Query and the "listener" middleware, and gives our current recommendations for what tools to use in different scenarios today.

The Evolution of Redux Async Logic - slides

The video should be online in the next few weeks, but for now you can see me give the talk as part of the Day 3 livestream:

The Evolution of Redux Async Logic - livestream video

TS Congress 2022: Lesson from Maintaining TS Libraries

Wed, 04 May 2022 11:00:00 -0500

I had the opportunity to give a talk at the first-ever Typescript Congress virtual conference.

My talk went over a variety of things I've learned working on the TypeScript aspects of the Redux libraries over the last few years. I covered things like different ways to include types when publishing, approaches for versioning public types APIs, supporting multiple TS versions, debugging and testing types, and some wacky examples of actual types from our libraries.

The recorded talk can be viewed on the TS Congress website:

Lessons from Maintaining TS Libraries - video

And the slides are here:

Lessons from Maintaining TS Libraries - slides

Presentations: Learn Modern Redux Livestream

Sat, 29 May 2021 16:00:00 -0500

This week I had the chance to appear on Jason Lengstorf's "Learn with Jason" livestream show.

The topic was "Learn Modern Redux". We started by recapping some of the usual topics ("what is Redux?", "why do some people dislike Redux?", "how has Redux changed?"), and then dove into live-coding a real Redux app. We showed how to create a new React+TS project using the Vite build tool (similar to Create-React-App), add the Redux packages, and set up Redux Toolkit and React-Redux from scratch (including our recommended TS hooks configuration).

We then showed how to use the upcoming RTK Query data fetching API to request a list of dog breeds from a public API, and display that data in our UI.

I had a blast being on this show, and I think it was a great chance to show folks how we recommend writing Redux code today.

The episode page on the "Learn with Jason" site has the embedded video, transcript, and show notes links:

Learn Modern Redux - episode page, video embed, and transcript

The example app is available as a live demo and the source is in a Github repo:

Running app: https://lets-learn-redux-toolkit.netlify.app/
Source code: https://github.com/learnwithjason/lets-learn-redux-toolkit

Presentations: The State of Redux, May 2021

Sat, 29 May 2021 16:00:00 -0500

I've done several prior iterations of my "State of Redux" talk, including:

I recently had a chance to record an updated version of the talk for an internal conference, and have posted the video for this one myself.

This iteration of the talk featured updates to the section on Redux Toolkit, an introduction to RTK Query, and info on how we recommend using Redux and TypeScript together.