I am trying react based on create-react-app. I'm new to react.
index.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
ReactDOM.render(
<App />,
document.getElementById('root')
);
./App in import App from './App'; is not clear to me when and where is this created, is this done by babel?
file strucutre
my-app/
README.md
node_modules/
package.json
.gitignore
public/
favicon.ico
index.html
src/
App.css
App.js
App.test.js
index.css
index.js
logo.svg
App.js
import React, { Component } from 'react';
class App extends Component {
render() {
return (
<div>myComponent</div>
)
}
}
export default App;
tl;dr
No, it is not done by Babel, instead it is done by create-react-app package.
All the files and folders in that folder are created automatically when you run,
create-react-app your-new-app-name
import App from './App'
The above line is used for importing the class you have written in the file App.js under the same directory.
Next, the difference between,
import App from './App'
and
import App from 'App'
Use the first if you want to import any user defined files and second for importing packages. As Shubham Khatri mentioned, for importing files, it is technically same if you did or did not use .js extension.
The longer version
create-react-app is a starter kit for people who are new to React or for who are lazy enough to build an app from scratch. What create-react-app does is, it will give you a minimal running React app with a solid folder structure. As given in their documentation, you can install that globally by giving,
npm install -g create-react-app
After this whenever you want to create a new app, what you want to do is,
create-react-app your-new-app-name
This will automatically generate a folder with all the files you mentioned.
Within the folder when you open the file public/index.html, you can see a line
<div id="root"> </div>
And on the src/index.js, you can find,
ReactDOM.render(
<App />,{}
document.getElementById('root')
);
If you are familiar with javascript, you may know that document.getElementById('root') is used to match any tag in HTML with ID as root. So the above snippet means that, they are rendering the <App> component of react to div with ID root. This is how React communicates with HTML page.
Rather that writing all the component codes in a single file, it is a good standard to write each components in different files. Here, App.js is a component that basically renders the text myComponent. For using this component in other files, you have to do two things.
Export the component from the file where it is defined. (export default App;)
Import the component to the file where it is used. (import App from './App')
General syntax for import is,
import className, { functionName } from 'packageName'
or
import className, { functionName } from './path-to-file/fileName'
Note: It is that ./ which tells the compiler whether to look on to node_modules folder or the path you mentioned. Use that strictly when you need to import user defined files.
Hope this helps!
When you import your Component like
import App from './App';
It will import your file App.js that is present in the same direcotry as index.js
In webpack configuration we specify which types of files babel needs to build and there if we specify .js or .jsx, it takes by default the extension of the file when we import it. we do not explicitly mention it. You can change your immport to be like
import App from './App.js';
which is technically the same.
The create-react-app npm package makes use of webpack to build your code which you can see from the package/react-scripts/package.json in the github directory
Related
I hope someone can tell me where I am going wrong in trying to get usable libraries
I have created a NPM project using create-react-app --format typescript, I then created the following structure:
|->tsconfig.json
|->package.json
|->config
|->tsconfig.base.json
|->tsconfig.cjs.json
|->tsconfig.esm.json
|->src
|->index.tsx
|->components
|->index.ts
|->ExampleComponent
|->ExampleComponent.component.tsx
|->ExampleComponent.stories.tsx
|->ExampleComponent.types.ts
|->index.ts
In this example the Example Component looks something like the following:
|->tscon
import React, { FC } from 'react';
// Contact specific icons
import Container from 'react-bootstrap/Container';
// Footer Properties
import { ExampleProperties } from './ExampleComponent.types';
export const ExampleComponent: FC<ExampleProperties> = ({ text }) => {
return (<Container fluid>{text}</Container>);
};
for the tsconfig files in 'config' I've lifted the Synk recommendation directly, while tsconfig.json is fairly simple like so:
{
"extends": "./configs/tsconfig.esm.json",
}
If I start the application via 'npm start' I get a website and the component correctly appears, but the issue is trying to import into another project.
I using npm link and npm link #Example/ExampleProject to bring the project in to another website and the index.tsx of that project looks like so:
import React from 'react';
import { createRoot } from 'react-dom/client';
import { ExampleComponent } from '#Example/ExampleProject';
const container = document.getElementById('root');
if (!container) throw new Error('Failed to find the root element') const root = createRoot(container);
root.render(
<React.StrictMode>
<main role={"main"} >
<ExampleComponent/>
</main>
</React.StrictMode> );
But when it starts I am getting this error:
Module not found: Error: Can't resolve './ExampleComponent/index' in '/home/user/IdeaProjects/ExampleProject/dist/esm' Did you mean 'index.mjs'? BREAKING CHANGE: The request './Common/index' failed to resolve only because it was resolved as fully specified (probably because the origin is strict EcmaScript Module, e. g. a module with javascript mimetype, a '*.mjs' file, or a '*.js' file where the package.json contains '"type": "module"'). The extension in the request is mandatory for it to be fully specified. Add the extension to the request.
The only thing I can think is tsc generates src/components/index.ts as a /src/component/index.js (which I rename). But ExampleComponent has .js and .mjs files within its directory
I am newbie to react js. After I setup the project folder to start coding I deleted the src folder and recreated it. Inside the src I created index.js and import all react libraries. But I am not seeing my hello world rendered on the localhost:3000 page. What could be the reason?
import React, { Component } from 'react';
import ReactDOM from 'react-dom';
class Index extends Component {
render(){
return(
<div><h1>hello world</h1></div>
)
}
}
ReactDOM.render(<Index />, document.getElementById('root'));
Delete your project folder
You then reinitiate npx create-react-app appname since you've not codded any logic yet, you've probably deleted a needed dependency file
When cleaning the hello world, don't delete the whole src folder. Just delete the files in the src folder except for the app.js and index.js
I have created component folder in src folder and tried to write simple greeting program for that I have created 3 files:
GreetUser.jsx
index.jsx
index.html
while compiling it is showing that could not find required index.js file.
I have written 3 files in Component folder and have imported GreetingUser module in the index.jsx file and while compiling it is showing that could not find required index.js file.
1.GreetingUser.jsx
import React , {component} from 'react';
class GreetUser extends component
{
render()
{
return <h1>Greetings from suraj!!!!</h1>;
}
}
export default GreetUser;
2.index.jsx
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import '../node_modules/bootstrap/dist/css/bootstrap.min.css';
import * as serviceWorker from './serviceWorker';
import GreetUser from './Component/GreetUser.jsx';
ReactDOM.render(<GreetUser/>,document.getElementById('aaa'));
serviceWorker.unregister();
Could not find a required file.
Name: index.js
Fundamentally, JSX just provides syntactic sugar for the React.createElement(component, props, ...children) function.
index file must with .js extension and not jsx is not react component.
index.js file in a folder lets you perform an import from the folder implicitly without specifying the index.js in the import statement – just like how web servers will serve up the index.html in a folder without you needing to explicitly put the index.html in the URL.
You can modify webpack configuration if you need it.
You can look at additional answers: Renaming index.js to index.jsx in react app and Why does create-react-app creates both App.js and index.js?
I am suffering compile failure using "create-react-app". The message I've gotten is as below.
__
./src/App.js
Module not found: You attempted to import /Contact which falls outside of the project src/ directory. Relative imports outside of src/ are not supported. You can either move it inside src/, or add a symlink to it from project's node_modules/.
__
Weird thing is that I certainly have "/Contact" file inside of src folder while The message says that I don't. Here is my folder tree.
And here is my App.js code.
import React, { Component } from 'react';
import PhoneForm from './components/PhoneForm';
class App extends Component {
render() {
return (
<div>
<PhoneForm />
</div>
);
}
}
export default App;
Feels like I am missing some kind of basic setting here.
Please have mercy on me and help me to figure this out.
If your App.js is in components folder, then you should use
import PhoneForm from './PhoneForm';
Note that you don't have to prepend the import with ./components.
But I don't see your PhoneForm component here altogether. So this might also be the source of error.
I have a bunch of React components in a folder and I can import each one individually like this:
import Component1 from '../components/component1/component1';
import Component2 from '../components/component2/component2';
Using the components like this works fine. However, when I bundle all the components using Webpack, the following code returns an empty object when I try to import the component.
import Component1 from '../dist/bundle.js';
I can't render this component. How do I export the components when bundling files?
Simply put you cannot import any modules from a bundle.
You need to include this code inside the source and then bundle it together
Actually you can do that. In my situation I needed react components in backbone application so what I did:
In react exposed components that should be importable by exporting them in entry point (usually index.js) like:
import React from 'react';
import ReactDOM from 'react-dom';
import Header from './components/Header/Header';
export {
React,
ReactDOM,
Header
};
Made my bundle output as library:
output: {
path: /some/path/of/your/lib,
library: 'reactapp',
libraryTarget: 'umd',
filename: `app${jsExtension}`,
},
Then bind name to file path in requirejs config:
reactapp: '/some/path/of/your/lib/app.js'
Then in code I can import that bundle as reactapp like:
define(["reactapp"], function(reactapp) {
// reactapp is object containing React, ReactDOM, Header
});