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npm Scripts and Your First React Component – Running the App, Building for Production, and Understanding Component Structure

This article introduces the npm scripts defined in your React project’s package.json file, which are used to run, build, and lint your application. It also walks through your first React component in App.jsx, simplifying it to focus on the fundamentals of JSX, function components, and variable scope inside and outside the component.

JSXnpmscriptsReact component

~2 min read · Updated Oct 21, 2025

npm Scripts in React


After understanding the folder structure, let’s explore the npm scripts defined in your package.json file. These scripts typically look like this:


"dev": "vite",
"build": "vite build",
"lint": "eslint .",
"preview": "vite preview"

You can run them using npm run <script> in your terminal:


  • npm run dev: Runs the app locally in development mode
  • npm run lint: Checks for code style and syntax issues
  • npm run build: Builds the app for production
  • npm run preview: Previews the production build (requires npm run build first)

Your First React Component


The first React component is defined in src/App.jsx. It’s a JavaScript function written in PascalCase and is known as a function component.


Simplified version to get started:


function App() {
  return (
    

      
Hello React

    

  );
}
export default App;

To start fresh, you can clear the contents of App.css and index.css.


Key Concepts in Components


  • Component names must start with a capital letter to be recognized by React.
  • Initially, the component has no parameters, but later you’ll learn about props.
  • The returned code looks like HTML but is actually JSX — a syntax that blends JavaScript and HTML.

Internal vs External Variables


Variables declared inside the function are redefined on every render. If a variable doesn’t depend on anything inside the component, it’s better to define it outside:


const title = 'React';
function App() {
  return (
    

      
Hello {title}

    

  );
}
export default App;

This avoids unnecessary redefinition and improves performance.


Conclusion


npm scripts help you run, build, and test your React project efficiently. By starting with a simple function component, you can focus on learning JSX, component structure, and variable scope. As you progress, you’ll explore props, state, and more advanced patterns in React.


Written & researched by Dr. Shahin Siami

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