Import on Component or Import on App.js/ts

Level 58

When deciding whether to import components like Head and Link directly within each component or globally in app.js/app.ts, there are several factors to consider: performance, clean code, and readability.

Performance

From a performance standpoint, there is generally no significant difference between importing components globally or locally. Modern JavaScript bundlers like Webpack or Vite are quite efficient at handling imports, and they will only include the necessary code in the final bundle. However, importing components globally can slightly increase the initial load time if the components are not used on every page.

Clean Code and Readability

Local Imports (Per Component):
- Pros:
  - Explicitness: It's clear which components are being used in each file, making it easier to understand dependencies.
  - Isolation: Each component is self-contained, which can make it easier to refactor or remove components without worrying about global dependencies.
- Cons:
  - Repetition: You have to import the same components in multiple files, which can be repetitive.
Global Imports (In app.js/app.ts):
- Pros:
  - Convenience: You only need to import components once, and they are available throughout your application.
  - Less Boilerplate: Reduces the need to repeatedly import the same components in multiple files.
- Cons:
  - Implicit Dependencies: It can be less clear which components are being used in a specific file, potentially making the code harder to understand.
  - Potential for Unused Imports: You might end up with components loaded globally that are not used everywhere, which can lead to unnecessary code in your bundle.

Recommendation

For most projects, especially larger ones, it's generally better to import components locally within each component file. This approach promotes better modularity and makes the codebase easier to maintain and understand. However, for utility components that are used in almost every component, such as a Button or Input, you might consider global imports to reduce boilerplate.

Here's an example of how you might structure your imports:

Local Import Example

// In MyComponent.js
import React from 'react';
import { Head, Link } from 'some-library';

const MyComponent = () => {
  return (
    <div>
      <Head title="My Page" />
      <Link to="/home">Home</Link>
    </div>
  );
};

export default MyComponent;

Global Import Example

// In app.js
import React from 'react';
import { Head, Link } from 'some-library';

const App = () => {
  return (
    <div>
      <MyComponent />
    </div>
  );
};

export default App;

// In MyComponent.js
import React from 'react';

const MyComponent = () => {
  return (
    <div>
      <Head title="My Page" />
      <Link to="/home">Home</Link>
    </div>
  );
};

export default MyComponent;

Ultimately, the choice depends on your project's specific needs and your team's preferences.