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Kent C. Dodds - Building React Apps Part 1

Planted March 31, 2020

This is the 3rd of 8 workshops and is a new one for Kent. He kicked off and was aware the timings might be a bit off because this is the first time through. This is going to be a big one and there is probably enough in the exercises that he didn’t think we’d get to those in the extra credit.

Timing was an issue and unfortunately the service worker he had developed for the course was playing up in his local environment. That didn’t get in the way of some excellent instruction and helpful learnings until right near the end.

Bootstrap the App

We are diving right in from a bare CRA. The task was simple enough - render a heading and some button to the screen.

We added a Dialog, using @reach/dialog which was small and fun. Kent reckons that code base is a good one to learn from. https://github.com/reach/reach-ui

It might be interesting to have a look at the code base and think about why it is effective and what patterns I could use. One of the upcoming workshops is on React patterns, so that will probably useful in this context.


Kent presents an opinionated approach to React. He is sharing what he thinks is the best approach based on his experience in production and teaching. He suggests using emotion and CSS-in-JS. He likes Tailwind and almost taught with that but decided at the last moment to stick with this as it was potentially too much to learn.

I’m a Tailwind fan too but this was my first exposure to emotion.

There are two ways to use emotion. You can create a styled component:

import styled from '@emotion/styled'

const Button = styled.button`
  color: turquoise;

You can use object notation

const Button = styled.button({
  color: 'turquoise',

Or you could even pass a function that will return the styles:

const Button = styled.button(props => {
  return {
    color: props.primary ? 'hotpink' : 'turquoise',

// or with the string form - as long as what you return is valid css

const Button = styled.button`
  color: ${props => (props.primary ? 'hotpink' : 'turquoise')};

This library allows us to use hover states and pseudo selectors which is one drawback of Tailwind.

The second way to use it is with the CSS prop - which means you can avoid single use components (Wrapper, Container, etc). This is similar to the inline styles prop but you can use the pseudo-selector.

You have to override the JSX parser and then use the css prop either with the object or css syntax.

This at the top of every relevant file:

/** @jsx jsx */
/** @jsxFrag React.Fragment */
import { jsx } from '@emotion/core'
import React from 'react'

and then you can do this:

function SomeComponent() {
  return (
        backgroundColor: 'hotpink',
        '&:hover': {
          color: 'lightgreen',
      This has a hotpink background.

// or with string syntax:

function SomeOtherComponent() {
  const color = 'darkgreen'

  return (
        background-color: hotpink;
        &:hover {
          color: ${color};
      This has a hotpink background.

This was a longer exercise and I didn’t get a chance to finish it up before Kent called us back from our breakout rooms.

In the styled component, you can pass in as many CSS objects as you like. It will use something like Object.assign and so the latter the object the more priority it will have.

With emotion, we can opt back into the CSS cascade and pass on some styles to children of a similar type.

        display: 'flex',
        flexDirection: 'column',
        alignItems: 'stretch',
        '> div': {
          margin: '10px auto',
          width: '100%',
          maxWidth: '300px',

Importable Babel plugins are something that Kent helped develop and allow for customisation of the parsing, building and printing processes. Emotion provides a plugin for their version of JSX (which basically just adds support for the CSS prop). The emotion styled/macro variant attaches the name of the component to the classname allowing you to trace where the styling is coming from. This is really helpful for debugging.

Media-queries and variables are all available. So stop hankering for SASS! :)

Data fetching

We are behind time and we’re going super fast now. Kent introduces the concept of having a API client handler. This means that you don’t have to deserialize the data every time and can abstract some of those details away.

Having a hook that encapsulates some of the logic makes things more managable and useful.

What was helpful for me here was thinking about tidying up my components by extracting this data logic to a single point. No longer changing res => res.json() on every call. Now it’s been pointed out it feels really obvious but that’s true with most insightful insights :)


There are lots of different ways to authenticate - basically you need to be able to deal with your backend.

There was a lot in this section - I need to review this again. I’m thinking a lot about applications I’m writing at the moment and there are lots of things here that would be useful to implement immediately.

Full page refresh:



This is using React Router 6 which is in beta at the moment but is likely to be released very soon.

The router doesn’t have to be top level - we can keep it at the least common parent and, in this case, just wrap the AuthenticatedApp.

The BrowserRouter provides the Context.Provider that is needed to pass the props between the various components of react-router.

href -> to

Redirect component needs a from prop.

Cache Management

Kent points out that cache management can be grouped into two buckets:

  1. UI state
  2. Server cache

When these are conflated, we can introduce unnecessary complexity. Given that caching is one of the hardest problems in software development, that’s not a good thing :)

Kent suggests react-query as a good solution for managing the server cache. It provides hooks to query, cache and mutate data in a way that is flexible enough for most use cases.

Time was running out for this exercise and Kent ran a poll - most wanted Kent’s explanations and talk-through. This is where the service worker was really playing up and so it was more challenging to follow.

I took an hour to do this exercise myself after the workshop.

The components had to be swapped out in a lot of places, so this exercise hit a lot of files. But, the main crux of the change was in creating a listItems client.

I really liked how this was set up.

Firstly, there was a listItemsClient - this had the specific CRUD operations for this data type.

Then, a list-items file was used to gather the hooks that made use of those client operations. They aren’t handled explicitly but instead are carried out by the useMutation hook from react-query.

These hooks are then brought into the components and the update/create/delete are destructured from the array returned from the useMutation.

So, in the component we see the things we want (update, create, delete). In the client, we see the explicit CRUD operations and the hooks file holds it all together.

This was an awesome section but probably could have been a workshop on it’s own! :)

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