I am newly learning the React Js. I found the example at this Link. But when I tried the first code:
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
import ReactDOM from 'react-dom';
class HelloMessage extends React.Component {
render() {
return (
<div>
Hello {this.props.name}
</div>
);
}
}
ReactDOM.render(
<HelloMessage name="Taylor" />,
mountNode
);
export default HelloMessage;
I am getting this error
./src/App.js Line 18: 'mountNode' is not defined no-undef
Search for the keywords to learn more about each error.
I have already seen the answer at this StackOverflow link. But I'm sorry I couldn't get what is explained there. Provide me the suggestions. Thank you in advance!
The error message you are getting is a linting error. (static code analysis)
Make sure your mountNode variable exists.
or use something like:
render(<HelloMessage />, document.getElementById('app'));
Also make sure that you have a DOM element with id app in your HTML code:
for example:
<div id="app" />
The ReactDOM.render() method is already located under
src/index.js
like:
ReactDOM.render(<App />, document.getElementById('root'));
registerServiceWorker();
The above code renders over component in the root div located in the public/index.html
src/App.js
--->initially it looked like:
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
class App extends Component {
render() {
return (
<div className="App">
<header className="App-header">
<img src={logo} className="App-logo" alt="logo" />
<h1 className="App-title">Welcome to React</h1>
</header>
<p className="App-intro">
To get started, edit <code>src/App.js</code> and save to reload.
</p>
</div>
);
}
}
export default App;
Finally --> Now instead of rendering the App Component...we can either write the HelloMessage component under the same file or replace the App Component with something like this..
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
class App extends Component {
render() {
return (
<div className="App">
<div>
Hello {this.props.name}
</div>
</div>
);
}
}
After that I'm able to see the Hello Message in the browser localhost:3000. But the Name Taylor is not displayed there...So what I did is passed the name props from the index.js file something like:
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import registerServiceWorker from './registerServiceWorker';
//Passed the name props to the
ReactDOM.render(<App name = "Taylor"/>, document.getElementById('root'));
registerServiceWorker();
Now After this point I got the successful output Hello Taylor. If you are replacing the App component with HelloMessage component, don't forget to import that file in the index.js
Related
I just started learning React but I can't for the life of me figure out how to link a new file to the App.jsx file. I've seen related questions but the setups are all quite different to mine. I used the default Vite template provided (for the most part). I've provided simple snippets of code below.
App.jsx code below:
import React from 'react'
import { useState } from 'react'
import './App.css'
import Pets from './components/Pets'
function App() {
return (
<div className="App">
<Animals/>
</div>
)
}
export default App
The page I'd like to link:
import React from 'react'
function Animals() {
return(
<div>
<h3>Pets for Africa</h3>
<ul>
<li>dogs</li>
<li>cats</li>
</ul>
</div>
)
}
export default Animals
The default main.jsx file which is part of the Vite template
import React from 'react'
import ReactDOM from 'react-dom/client'
import App from './App'
import './index.css'
ReactDOM.createRoot(document.getElementById('root')).render(
<React.StrictMode>
<App />
</React.StrictMode>
)
Change the default import's name to Animals
import React from 'react'
import { useState } from 'react'
import './App.css'
import Animals from './components/Pets'
function App() {
return (
<div className="App">
<Animals/>
</div>
)
}
export default App
This should work in your case.
Aren't you trying to import file Pets which has name Animals? If yes, simply rename the import Pets from './components/Pets' to import Animals from './components/Animals'
I'm very new to React and ran into an issue when trying to import a "sub-component", for lack of a better word.
In my App.js file I imported my header class: import Header from './Components/Header/Header'; Which worked fine.
Within my Header.js file I'm using router to select different components. However, when I try to import my Home class: import Home from '../Subcomponents/HomePage/HomePage'; I receive the following error: Module not found: Can't resolve '../Subcomponents/HomePage/HomePage'
My file structure is:
app.js
Components/Header/Header.js
Subcomponents/HomePage/HomePage.js
App.js Code:
import React, { Component } from 'react';
import Header from './Components/Header/Header';
import Footer from './Components/Footer/Footer';
import Body from './Components/Body/Body';
import './Assets/css/mainCSS.css';
class App extends Component {
render() {
return (
<div className="App">
<Header />
<Body />
<Footer/>
</div>
);
}
}
export default App;
Header Code:
import React from 'react';
import Home from '../Subcomponents/HomePage/HomePage';
import { Router, Route, Link } from 'react-router-dom';
const header = () => {
return <header>
<Router>
<nav>
<ul>
<li>
<Link to='/'>Home</Link>
</li>
</ul>
<hr />
<Route excat path ="/" component={Home} />
</nav>
</Router>
</header>
}
export default header;
HomePage Code:
import React from 'react';
const homepage =() =>{
return <p>
homepage working
</p>
}
export default homepage;
Am I doing something wrong here or is this not possible in React? Any advice would be greatly appreciated!
Thanks!
From Header.js, ../ puts you into Components, not into the parent. It should be '../../Subcomponents/HomePage/HomePage'.
Also, imho: within each component folder, name the file index.js so that it will be automatically exported. Than you can just do: '../../Subcomponents/HomePage'
I'm trying to create a React component for a navigation bar.
This component I'd like to import from a separate file into my App.js.
Currently, the component should just return a simple 'Hello world' paragraph, but I have trouble getting this to work.
I have written the following code into a file located at src/components/navbar.js:
import React from 'react';
export default class navBar extends React.Component {
render() {
return (
<p>Hello world.</p>
)
}
}
Now I'd like to import this component from my src/App.js, which looks like this:
import React, { Component } from 'react';
import './App.css';
import navBar from './components/navbar.js'
class App extends Component {
render() {
return (
<navBar/>
);
}
}
export default App;
If I compile and open the site, nothing's there, which confuses me.
I'd be very thankful for any help!
EDIT:
It's been suggested that the problem is that <App /> is not being rendered anywhere. I don't believe that's the case, since there's another file being created by default (index.js), which looks like this:
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';
ReactDOM.render(<App />, document.getElementById('root'));
serviceWorker.unregister();
I have also tried putting the paragraph (and the entire navbar) directly into src/App.js.
After compiling I could see the expected results in the browser, so the problem should lie with the exporting/importing.
In JSX, lower case tags are considered to be simple HTML/SVG elements. You can use lower case only if you use accessors (so with a dot like bla.blabla).
You can read about it here for example.
So in your case you must change the class name navBar to NavBar and then in the render method:
render() {
return (
<NavBar/>
);
}
Here is a full working example:
** Note: NavBar.js shoud start with a Capital letter.
App.js
import React from "react";
import ReactDOM from "react-dom";
import NavBar from "./components/NavBar";
function App() {
return (
<div className="App">
<NavBar />
</div>
);
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
NavBar.js
import React from "react";
export default class NavBar extends React.Component {
render() {
return (
<div>
<p>Hello world.</p>
</div>
);
}
}
I have a ReactJS basic project which is working fine with the following two files (among others):
Header.js
import React from 'react'
const Header = () => (
<div>THIS IS A HEADER</div>
)
export default Header
App.js
import React, { Component } from 'react'
import ReactDOM from 'react-dom'
import Header from './Header'
class App extends Component {
render() {
return (
<div>
<Header />
<div>
Hello World! This is the content.
</div>
</div>
)
}
}
ReactDOM.render(<App />, document.getElementById('app'))
What I want to know is:
How can I reference the Header component with a custom tag, for example: <comp-header /> instead of: <Header />. Something like below:
App.js
import React, { Component } from 'react'
import ReactDOM from 'react-dom'
import Header from './Header'
class App extends Component {
render() {
return (
<div>
<comp-header />
<div>
Hello World! This is the content.
</div>
</div>
)
}
}
ReactDOM.render(<App />, document.getElementById('app'))
Any idea on how to do that?
Thanks!
You can simply
import CompHeader from './Header'
and use normally.
I don't think you can use a dash in JSX and JSX elements that are non native elements need to be capitalized.
I have recently installed Material UI into my Meteor application using npm install --save material ui
I have gotten the <Header /> component showing up in my app.js file, but whenever I add other components, localhost:3000 simply displays a blank page. Please see my code below:
header.js
import React, { Component } from 'react';
import AppBar from 'material-ui/AppBar';
class Header extends Component {
render() {
return(
<AppBar
title="Header"
titleStyle={{textAlign: "center"}}
showMenuIconButton={false}
/>
);
}
}
export default Header;
app.js
import React from 'react';
import ReactDOM from 'react-dom';
import MuiThemeProvider from 'material-ui/styles/MuiThemeProvider';
import Header from './components/header';
import NewPost from './components/new_post';
const App = () => {
return (
<MuiThemeProvider>
<Header />
</MuiThemeProvider>
);
};
Meteor.startup(() => {
ReactDOM.render(<App />, document.querySelector('.render-target'));
});
THE ABOVE CODE WORKS WELL (see screenshot below)
However, if I add another component I get a blank screen
header.js is the same
new_post.js
import React, { Component } from 'react';
import TextField from 'material-ui/TextField';
class NewPost extends Component {
render() {
return (
<TextField
hintText="Full width"
fullWidth={true}
/>
);
}
}
export default NewPost;
app.js
import React from 'react';
import ReactDOM from 'react-dom';
import MuiThemeProvider from 'material-ui/styles/MuiThemeProvider';
import Header from './components/header';
import NewPost from './components/new_post';
const App = () => {
return (
<MuiThemeProvider>
<Header />
<NewPost />
</MuiThemeProvider>
);
};
Meteor.startup(() => {
ReactDOM.render(<App />, document.querySelector('.render-target'));
});
The result is simply a blank screen
Why does adding one more component (<NewPost />)inside of <MuiThemeProvider> result in a blank screen? I referred to the material-ui documentation and their sample projects but their application structure is not similar to mine. Any advice? Please let me know if you need more info to make this question clearer.
Wow very strange but I managed to get it working by simply adding a <div>
app.js
const App = () => {
return (
<MuiThemeProvider muiTheme={getMuiTheme()}>
<div>
<Header />
<NewPost />
</div>
</MuiThemeProvider>
);
}
Meteor.startup(() => {
ReactDOM.render(<App />, document.querySelector('.render-target'));
});
I would really appreciate if anyone could explain why adding a div makes this all work. Thank you!
I would really appreciate if anyone could explain why adding a div
makes this all work
If you look at the browser warning, "Invalid prop children of type array supplied to MuiThemeProvider, expected a single ReactElement.".
So, when you add a <div/> around your components, it wraps them together and turns them into a single react element.
MuiThemeProvider renders as null so you have to wrap children do anything - for example React.Fragment