This project was done for 'Meta Front-End Developer Professional Certificate' and demonstrates the simplest React App and how to test it using 'React Testing Library' for simple testing.
useState hook can work with primitive (string) data and with complex data (state stored in objects) In this project, state is stored in a primitive data string.
// declare
const [result, setResult] = useState(0);
// update for a primitive data string
setResult((result) => result + Number(inputRef.current.value));
// for example, declare complex data
const [giftCard, setGiftCard] = useState(
{
firstName: "Jennifer",
lastName: "Smith",
text: "Free dinner for 4 guests",
valid: true,
instructions: "To use your coupon, click the button below.",
}
);
// for example, update complex data
function spendGiftCard() {
setGiftCard(prevState => {
return {
...prevState,
text: "Your coupon has been used.",
valid: false,
instructions: "Please visit our restaurant to renew your gift card."
}
});
}useRef hook helps your to persist values between renders.
It can be used to store a mutable value that does not cause a re-render when updated.
It can be used to access a DOM element directly.
// create
const inputRef = useRef(0);
// use
setResult((result) => result + Number(inputRef.current.value));
// render input
<input
id="input"
pattern="[0-9]"
ref={inputRef}
type="number"
placeholder="Type a number"
/>useEffect hook lets you synchronize a component with an external system or provide an external change to the app.
useEffect(() => {
document.body.style.background = theme === "light" ? "white" : "black";
}, [theme]);useTheme helps building Light/Dark theme on the app. Custom-made.
// import
import { useTheme } from "../ThemeContext";
// create
const { theme, toggleTheme } = useTheme();This math calculator was created using command:
npx create-react-app my-appThis project was bootstrapped with Create React App.
In the project directory, you can run:
Runs the app in the development mode.
Open http://localhost:3000 to view it in your browser.
The page will reload when you make changes.
You may also see any lint errors in the console.
Launches the test runner in the interactive watch mode.
See the section about running tests for more information.
Builds the app for production to the build folder.
It correctly bundles React in production mode and optimizes the build for the best performance.
The build is minified and the filenames include the hashes.
Your app is ready to be deployed!
See the section about deployment for more information.
Note: this is a one-way operation. Once you eject, you can't go back!
If you aren't satisfied with the build tool and configuration choices, you can eject at any time. This command will remove the single build dependency from your project.
Instead, it will copy all the configuration files and the transitive dependencies (webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except eject will still work, but they will point to the copied scripts so you can tweak them. At this point you're on your own.
You don't have to ever use eject. The curated feature set is suitable for small and middle deployments, and you shouldn't feel obligated to use this feature. However we understand that this tool wouldn't be useful if you couldn't customize it when you are ready for it.
You can learn more in the Create React App documentation.
To learn React, check out the React documentation.
This section has moved here: https://facebook.github.io/create-react-app/docs/code-splitting
This section has moved here: https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size
This section has moved here: https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app
This section has moved here: https://facebook.github.io/create-react-app/docs/advanced-configuration
This section has moved here: https://facebook.github.io/create-react-app/docs/deployment
This section has moved here: https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify