title: What's the difference between npm run dev and npm run start in Next.js?
body: <p>I am wondering what would the difference be between <code>npm run dev</code> and <code>npm run start</code>.
  To my surprise, I could not find much information online about this topic.</p>
  <p>Specifically, I'd like to know in the context of React and Next JS.</p>
  <p>I noticed that with React, you can start your app by running <code>npm run start</code>, without the need of running a build first. On the other hand, Next JS doesn't seem to behave in the same way (but I could have done something wrong with the setup).
  I tried running a new Next app using <code>npm run start</code>, as it's a default script in <code>package.json</code>, but it didn't work. It shows this error: <code>*Error: Could not find a production build*</code></p>
  <p>Instead, running <code>npm run dev</code> created a .next folder, and started the server on port 3000 with no issues.</p>
  <p>Can anyone help me understand how this works?</p>