You can have javascript code inside your components likewise

const Component = props => {
//javascript code
return (<div>-- Component JSX---</div>)
}

if the javascript code if just needed for the initializing of the component you can use react hooks to run a piece of code only one time after the component is created.

import React, { useEffect } from 'react';

const Component = props => {

useEffect(() => {
 // javascript code
}, [])

return (<div>--Component JSX---</div>
}

the empty array as second argument indicates the useEffect hook that the effect should only be ran once after the component has been initialized.

So the way React works is you will be building “HTML” using React functional/class components like this example

import React from 'react';
//Just like a normal javascript function, it listens to in this 
instance, the return statement. You're returning regular HTML.
function Navbar() {
  return (
    <div>This is some text built by react</div>
    <p>Saying hello to react by building a functional component</p>
  )
}

export default Navbar;  //This right here is exporting the file so it can be 
//used elsewhere just import it in other file.

So the return is where you will build your website, then in the next component you will import should look something like this.

Normally, it is called App.js or in some instances where it’s more complex it’s anythinng you want.

import Navbar from '../components/Navbar.js';

function App() {
  return (
    <Navbar /> //Now you don't have to write your main content in here you can 
               //just import it. Just like Navbar
    <div>This is my main content in page</div> 
  )
}

Hi guys hope you’re fine, I’m student and I have this year to do some thing like a project to end my studies , so I chose to create a website (using React/Django) I already have the site but made by HTML,CSS,bootstrap & JQuery , so now i have to convert it to react , but i have a problem i don’t know how to include some js files inside a components , every things else is going good, I need just what is in the js files to applied it in some components.
Hope you help me out.
cordially