what is the difference between [id].js and [...id].js and [[...id]].js ?

[utkarsh-1602]

• [id].js: For example, a blog could include the following route pages/blog/[slug].js where [slug] is the Dynamic Segment for blog posts.
• [...id].js: Dynamic Segments can be extended to catch-all subsequent segments by adding an ellipsis inside the brackets [...segmentName].
• [[...id]].js: Catch-all Segments can be made optional by including the parameter in double square brackets: [[...segmentName]].

[utkarsh-1602]

both [id].js and [...id].js are used for dynamic routing, but they serve slightly different purposes.

[id].js:

This is used for a single dynamic segment in the URL.
For example, if you have a route like /pages/blog/[id].js, it means that you can access the page with URLs like /blog/1, /blog/2, etc.The value captured by the dynamic segment (in this case, id) will be available as a parameter to the page component.

Example:

// pages/blog/[id].js
import { useRouter } from 'next/router';

const BlogPost = () => {
  const router = useRouter();
  const { id } = router.query;

  return <div>Blog Post {id}</div>;
};

export default BlogPost;

[utkarsh-1602]

[...id].js:

This is used for catching all subsequent segments in the URL.
For example, if you have a route like /pages/blog/[...id].js, it means that you can access the page with URLs like /blog/1, /blog/1/2, /blog/1/2/3, and so on.The values captured by the ellipsis notation will be available as an array in the id parameter.

Example:

// pages/blog/[...id].js
import { useRouter } from 'next/router';

const BlogPost = () => {
  const router = useRouter();
  const { id } = router.query;

  return <div>Blog Post {id.join('/')}</div>;
};

export default BlogPost;