Just a few weeks until the 2021 JavaScript Full-Stack Bootcamp opens.
Signup to the waiting list!
In this short tutorial we’ll build a very simple example of a counter in React, applying many of the concepts and theory outlined before.
Let’s use Codepen for this. We start by forking the React template pen.
In Codepen we don’t need to import React and ReactDOM as they are already added in the scope.
We show the count in a div, and we add a few buttons to increment this count:
const Button = ({ increment }) => {
return <button>+{increment}</button>
}
const App = () => {
let count = 0
return (
<div>
<Button increment={1} />
<Button increment={10} />
<Button increment={100} />
<Button increment={1000} />
<span>{count}</span>
</div>
)
}
ReactDOM.render(<App />, document.getElementById('app'))
Let’s add the functionality that lets us change the count by clicking the buttons, by adding a onClickFunction
prop:
const Button = ({ increment, onClickFunction }) => {
const handleClick = () => {
onClickFunction(increment)
}
return <button onClick={handleClick}>+{increment}</button>
}
const App = () => {
let count = 0
const incrementCount = increment => {
//TODO
}
return (
<div>
<Button increment={1} onClickFunction={incrementCount} />
<Button increment={10} onClickFunction={incrementCount} />
<Button increment={100} onClickFunction={incrementCount} />
<Button increment={1000} onClickFunction={incrementCount} />
<span>{count}</span>
</div>
)
}
ReactDOM.render(<App />, document.getElementById('app'))
Here, every Button element has 2 props: increment
and onClickFunction
. We create 4 different buttons, with 4 increment values: 1, 10 100, 1000.
When the button in the Button component is clicked, the incrementCount
function is called.
This function must increment the local count. How can we do so? We can use hooks:
const { useState } = React
const Button = ({ increment, onClickFunction }) => {
const handleClick = () => {
onClickFunction(increment)
}
return <button onClick={handleClick}>+{increment}</button>
}
const App = () => {
const [count, setCount] = useState(0)
const incrementCount = increment => {
setCount(count + increment)
}
return (
<div>
<Button increment={1} onClickFunction={incrementCount} />
<Button increment={10} onClickFunction={incrementCount} />
<Button increment={100} onClickFunction={incrementCount} />
<Button increment={1000} onClickFunction={incrementCount} />
<span>{count}</span>
</div>
)
}
ReactDOM.render(<App />, document.getElementById('app'))
useState()
initializes the count variable at 0 and provides us the setCount()
method to update its value.
We use both in the incrementCount()
method implementation, which calls setCount()
updating the value to the existing value of count
, plus the increment passed by each Button component.
The complete example code can be seen at https://codepen.io/flaviocopes/pen/QzEQPR
Download my free React Handbook
The 2021 JavaScript Full-Stack Bootcamp will start at the end of March 2021. Don't miss this opportunity, signup to the waiting list!
More react tutorials:
- A React simple app example: fetch GitHub users information via API
- Build a simple counter with React
- VS Code setup for React development
- How to pass props to a child component via React Router
- Create an app with Electron and React
- Tutorial: create a Spreadsheet using React
- The roadmap to learn React
- Learn how to use Redux
- Getting started with JSX
- Styled Components
- Introduction to Redux Saga
- Introduction to React Router
- Introduction to React
- React Components
- The Virtual DOM
- React Events
- The React State
- React Props
- The React Fragment
- The React Context API
- React PropTypes
- React concepts: declarative
- React: How to show a different component on click
- How to loop inside React JSX
- Props vs State in React
- Should you use jQuery or React?
- How much JavaScript you need to know to use React?
- Introduction to Gatsby
- How to reference a DOM element in React
- Unidirectional Data Flow in React
- React Higher Order Components
- React Lifecycle Events
- React Concept: Immutability
- React Concept: Purity
- Introduction to React Hooks
- Introduction to create-react-app
- React Concept: Composition
- React: Presentational vs Container Components
- Code Splitting in React
- Server Side Rendering with React
- How to install React
- CSS in React
- Using SASS in React
- Handling Forms in React
- React StrictMode
- React Portals
- React Render Props
- Testing React components
- How to pass a parameter to event handlers in React
- How to handle errors in React
- How to return multiple elements in JSX
- Conditional rendering in React
- React, how to transfer props to child components
- How to get the value of an input element in React
- How to use the useState React hook
- How to use the useCallback React hook
- How to use the useEffect React hook
- How to use the useMemo React hook
- How to use the useRef React hook
- How to use the useContext React hook
- How to use the useReducer React hook
- How to connect your React app to a backend on the same origin
- The Reach Router Tutorial
- How to use the React Developer Tools
- How to learn React
- How to debug a React application
- How to render HTML in React
- How to fix the `dangerouslySetInnerHTML` did not match error in React
- How I fixed an issue with a React login form state and Browser autofill
- How to configure HTTPS in a React app on localhost
- How to fix the "cannot update a component while rendering a different component" error in React
- Can I use React hooks inside a conditional?
- Using useState with an object: how to update
- How to move around blocks of code with React and Tailwind
- React, focus an item in React when added to the DOM
- React, edit text on doubleclick
- React Router, how to get data from a dynamic route
- React Router, why useLocation and useHistory might return undefined