Misc scribbles

The React tutorial I wish I had


When I was learning React, I found it very challenging, and my eyes would glaze over any time I tried to learn

Here is a short tutorial that could help you get started. Ultimately, for me, sitting down with a book was what finally helped me, but this blogpost aims to be a sort of TLDR for certain concepts.

#The simplest React component

Here is a "React component" that prints hello world in a div

function HelloWorld() {
  return <div>Hello world!</div>

I like to think of React components as "functions that return HTML". That is a oversimplification, but it can be a helpful thinking tool to help you get started.

#Using our HelloWorld component in another component

We said React can be thought of as "functions that return HTML" but we can also combine them together.

For example, we can create a component named "App" that uses our "HelloWorld" component

function App() {
  return (
      <p>This is my app</p>
      <HelloWorld />

It is common to have an "App" level component, that renders all the other components in your page

#How do these components get rendered to HTML?

Typically, just once in your app, you use ReactDOM to render the "App" level component to the page.

import ReactDOM from 'react-dom'
ReactDOM.render(<App />, document.getElementById('root'))

And in your index.html you have e.g.

<!doctype html>
    <div id="root" />

#Accepting parameters to your components

React components can accept "props" which are like parameters to your component

function Hello(props) {
  const name = props.name
  return <div>Hello {name}!</div>

We then pass props using HTML like attributes

function App() {
  return (
      <Hello name="Colin" />

This will print "Hello Colin!"

#Rendering lists of items

The {name} inside the div is a little snippet of plain-JS code. It can be used to do more complicated things. For example you can render a list of items

function List() {
  const list = ['Apples', 'Oranges', 'Pears']
  return (
      {list.map(item => (
        <li key={item}>{item}</li>

Inside the "list" each item has a key prop that is specified. See https://reactjs.org/docs/lists-and-keys.html for more discussion on this

#How do I use React in my own app?

Commonly, React is downloaded from npm using your package manager, but often requires some extra steps to get JSX to compile which is often done by babel. I will not cover a minimal React setup here, but I will recommend a couple setups that make it easy for starting out.

If you are trying to incorporate React into a legacy or existing project, then I encourage you to experiment in these starter kit environments first. It can be difficult to bolt on React to an existing environment in some ways and understanding the basics will help.


I hope this helps you get started with React, let me know if you have any questions.

#Footnote 1. Class based components

In the old days, React used "class based components", here is the Hello world example as a class based component

class HelloWorld {
  render() {
    return <div>Hello world!</div>

The class based components had other "lifecycle functions" like "componentDidMount" and such that do not exist in function based components. In function components, React hooks are used instead.

You will probably mostly see function components instead of class based components these days

#Footnote 2. How is this HTML allowed in React?

The HTML-like syntax may look odd in JS code. It is called JSX. So code like this:

function HelloWorld() {
  return <div>Hello world</div>

would get converted to this by babel or other jsx transpiler:

function HelloWorld() {
  // null just means no props to the div element
  return React.createElement('div', null, 'Hello world')

It's not common to write React without jsx, but as seen above, it can be done :)

#Footnote 3. Slightly changed in React 18

React 18 uses createRoot instead of ReactDOM.render and is a little bit more verbose, but I'm going for brevity here

#Footnote 4. Things that sometimes complicate your React learning experience

The React learning experience, when it's good, is quite nice. But there can be many roadblocks

#Footnote 5. Brief intro to useState

The component HelloWorld does not do much, it just does a div. How do you make dynamic content in React? One way is with React hooks like useState and useEffect.

function FormField() {
  const [value, setValue] = useState('Initial value')
  return <input value={value} onChange={evt => setValue(evt.target.value)} />

This is a 'controlled component' in React terms: we control the value that is displayed by the <input> box with the 'value prop' and any time the user types something, we run the setValue callback, and then it re-renders. Any time a 'setter' from the useState is called, React re-renders the component.

#Footnote 6. Brief intro to useEffect

The useEffect method can be thought of as saying: "as a side effect of rendering the component, do some stuff". You can use it to fetch data from an API for example, and so you'd say "as a side effect of rendering this component, go fetch some data from this API". Then you can combine it with a useState and make it re-render after the fetch has completed.


// I use this myfetch helper a lot, many examples with fetch neglect to handle
// !result.ok
async function myfetch(url: string) {
  const result = await fetch(url)
  if (!result.ok) {
    throw new Error(
      `HTTP ${result.status} fetching ${url} ${await result.text()}`,
  return result.json()
function FetchStuff() {
  const [data, setData] = useState()
  const [error, setError] = useState()
  useEffect(() => {
    ;(async () => {
      try {
        const result = await myfetch('/my/api')
      } catch (e) {
  if (data) {
    return <div>Got some data {JSON.stringify(data)}</div>
  } else if (error) {
    return <div style={{ background: 'red' }}>Error {`${error}`}</div>
  } else {
    return <div>Loading...</div>