HTTP requests with fetch

A server does not only answer requests — it sends them too: it fetches exchange rates, checks an address with an external service, posts a notification. Node.js has the same fetch() function as the browser for this, with nothing to install. You know how it works from the tutorial; here are the specifics of server code.

A GET request

Create the file scripts/check-blog.js, which requests your blog's post list. The server from the previous lessons must be running in another terminal window:

// scripts/check-blog.js
const response = await fetch('http://localhost:3000/posts');
const posts = await response.json();
 
console.log(`Posts in the blog: ${posts.length}`);

node scripts/check-blog.js prints the number of posts. await works directly in the module, and response.json() parses the response body.

Checking the status

fetch() does not throw on 404 or 500 responses — it throws only when the server cannot be reached at all. You check the status yourself with response.ok:

// scripts/check-blog.js
const response = await fetch('http://localhost:3000/posts/999');
 
if (!response.ok) {
  console.log(`Error: ${response.status}`);
} else {
  console.log(await response.json());
}

There is no post 999, so "Error: 404" is printed. response.ok is true for codes from 200 to 299.

Sending JSON

For a POST request you pass the method, a header and a string body:

// scripts/add-post.js
const response = await fetch('http://localhost:3000/posts', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ title: 'A post from a script', body: 'Sent with fetch' }),
});
 
const post = await response.json();
console.log(response.status, post.id);

It prints 201 and the new post's number — the same result as curl in the previous lesson.

Limiting the wait

If an external server hangs, fetch() waits a very long time. AbortSignal.timeout() aborts the request after the given number of milliseconds:

// scripts/check-blog.js
try {
  const response = await fetch('http://localhost:3000/posts', {
    signal: AbortSignal.timeout(3000),
  });
  console.log(response.status);
} catch (error) {
  console.log(`The server did not answer: ${error.name}`);
}

If there is no answer for three seconds, "The server did not answer: TimeoutError" is printed. If the server is not running, the error also lands in catch — named TypeError with the message fetch failed.

What the response offers

Common mistake

In the browser you can write fetch('/posts') because the address is completed from the current page. Node.js has no page, and a relative address causes an error:

TypeError: Failed to parse URL from /posts

Always pass the full address with protocol and host: http://localhost:3000/posts. The base address is convenient to keep in an environment variable.