This 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 the browser.
The page will reload if you make edits.
You will 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
How React render elements:
React.createElement("h1", null, "Heyy Engine!"),
First is what we want to put (h1), where we want to put(null), and content. Add property:
React.createElement("h1", {style: {color: "blue"}}, "Heyy Engine!"),
Add a ul:
React.createElement(
"ul",
null,
React.createElement("li", null, "Monday"),
React.createElement("li", null, "Tuesday"),
React.createElement("li", null, "Wednesday"),
React.createElement("li", null, "Thursday")
),
The above equivalents here:
ReactDOM.render(
<ul>
<li>Monday</li>
<li>Tuesday</li>
<li>Wednesday</li>
</ul>,
document.getElementById("root")
We have the following:
function App() {
return (
<div className="App">
<h1>Header</h1>
<h2>Main</h2>
<h3>Footer</h3>
</div>
);
}
And when we export default App; // That I need to import that to my index.js, we will import app under index.js to display it.
ReactDOM.render(
App(),
document.getElementById('root')
);
Now we want to replace header as a component:
function Header() {
return (
<header>
<h1>Eve's Kitchen</h1>
</header>
);
}
So under the app we can:
function App() {
return (
<div className="App">
<Header/>
<h2>Main</h2>
<h3>Footer</h3>
</div>
);
}
At the end we can have something as below:
function App() {
return (
<div className="App">
<Header/>
<Main/>
<Footer/>
</div>
);
}
How to add a property to your component It's always have a props (if nothing passed, it is an empty object):
function Header(props) {
// Always have a props and maybe an empty object
console.log(props);
return (
<header>
<h1>{props.name}'s Kitchen</h1>
</header>
);
}
In order to pass the property:
<Header name="Cindy"/>
In order to pass the data:
<section>
<p>We serve the most {props.adjective} food around.</p>
<ul style={{textAlign: "Left"}}>
{props.dishes.map((dish) => (
<li>{dish}</li>
))}
</ul>
</section>
The javascript will have textAlign (instead text-align following css).
When we do that, we have an error in the console.log:
index.js:1 Warning: Each child in a list should have a unique "key" prop.
Check the render method of `Main`. See https://reactjs.org/link/warning-keys for more information.
at li
at Main (http://localhost:3000/static/js/main.chunk.js:182:46)
at div
So add the id as below:
<ul style={{textAlign: "Left"}}>
{props.dishes.map((dish, i) => (
<li key={i}>{dish}</li>
))}
</ul>
Use fragments:
ReactDOM.render(
<div>
<App/>,
<AppTwo/>
</div>
,
document.getElementById('root')
);
(Wrapped them into a
so it won't have a problem). You can use fragment:ReactDOM.render(
<React.Fragment>
<App/>,
<AppTwo/>
</React.Fragment>
,
document.getElementById('root')
);
Or even no need the keyword "Fragment":
ReactDOM.render(
<>
<App/>,
<AppTwo/>
</>
,
document.getElementById('root')
);
First way to render conditional rendering:
ReactDOM.render(
<App authorized={true} />,
document.getElementById('root')
)
function App(props) {
if (props.authorized) {
return <SecretComponent/>
} else {
return <RegularComponent/>
}
}
Second way:
function App(props) {
return (
<>
{props.authorized ? <SecretComponent/> : <RegularComponent/>}
</>
);
}
Destructing arrays and objects
const [mostImportantItem] = ["boots", "tent", "headlamp"];
console.log(mostImportantItem);
It will take the first item which is "boots"
Understanding the useState hook
import React, {useState} from 'react';
function App() {
const [emotion, setEmotion] = useState("happy");
return (
<>
<h1>Current emotion is {emotion}.</h1>
<button onClick={() => setEmotion("happy")}>Happy</button>
<button onClick={() => setEmotion("frustrated")}>Frustrate</button>
<button onClick={() => setEmotion("enthusiastic")}>Enthuse</button>
</>
);
}
useState has 2 variables: 1 is state, 1 is the function. Working with useEffect Another important Hook that's part of the React library is useEffect. It's typically used to manage side effects that are not related to the components render. Things like console messages, loading data and sometimes animations can benefit from useEffect.
function App() {
const [emotion, setEmotion] = useState("happy");
useEffect(() => {
console.log(`It's ${emotion} around here!`);
})
return (
<>
<h1>Current emotion is {emotion}.</h1>
<button onClick={() => setEmotion("happy")}>Happy</button>
<button onClick={() => setEmotion("frustrated")}>Frustrate</button>
<button onClick={() => setEmotion("enthusiastic")}>Enthuse</button>
</>
);
}
This allows us to do something that doesn't have to do with the render of the component, but it's just a side effect. useEffect takes in a second argument and this argument called the dependency array.
useEffect(() => {
console.log(`It's ${emotion} around here!`);
}, [emotion])
I'm going to pass emotion into this dependency array to keep tracks of values. NOw I can see everytime this being updated. so useEffect is going to watch this state value if it changes it will call the function.
Incorporating useReducer Let's consider a checkbox and how we might manage it say using react.
function App() {
const [checked, toggle] = useReducer(
(checked) => !checked,
false
);
return (
<>
<input type="checkbox" value={checked} onChange={toggle}/> // Instead set the whole function, we can send the name of the function here
<p>
{checked ? "checked" : "not checked"}
</p>
</>
);
}
A reducer function's most simple definition is it takes in the current state and it returns a new state. If checked is false, it should return the opposite, which is true.
Fetching data with Hooks We're going to grab some data from Github API. If I go to api.github.com/users, this will give me a list of all the GitHub users and their data as JSON.
function App({login}) {
const [data, setData] = useState(null);
useEffect(() => {
fetch(`https://api.github.com/users/${login}`)
.then((response) => response.json())
.then(setData);
}, []);
if (data) {
return (
<>
{JSON.stringify(data)}
</>
);
} else {
return (
<> No data is found </>
)
}
}
Handling loading states When we make an HTTP request to an API, there are 3 possible states: pending loading, success and failed. A lot of times if we make our requests to a broken URL, we just have empty screen and we want to let users know that something has gone wrong.
function App({login}) {
const [data, setData] = useState(null);
const [loading, setLoading] = useState(false);
const [error, setError] = useState(null);
useEffect(() => {
if (!login) return;
setLoading(true);
fetch(`https://api.github.com/users/${login}`)
.then((response) => response.json())
.then(setData)
.then(() => setLoading(false))
.catch(setError);
}, [login]); // everytime the value is changed we will call it
if (loading) return <h1>Loading...</h1>;
if (error) return <pre>{JSON.stringify(error, null, 2)}</pre>;
if (!data) return null;
{
return (
<>
<h1>{data.name}</h1>
<p>{data.location}</p>
<img alt={data.login} src={data.avatar_url}/>
</>
);
}
}
Any files ends in .test.js is going to be through of as a test.