The way to use the Fetch API in Node.js, Deno, and Bun — SitePoint

On this article, we’ll take a look at the way to use the Fetch API with Node.js, Deno, and Bun.

Fetch API vs XMLHttpRequest

Fetching information through an HTTP request is key net utility exercise. You could have made such calls within the browser, however the Fetch API is natively supported in Node.js, Deno, and Bun.

In a browser, you may request data from a server so you possibly can show it with no full display screen refresh. That is sometimes often known as an Ajax request or a single web page utility (SPA). Between 1999 and 2015, XMLHttpRequest was the one choice — and stays so if you wish to present file add progress. XMLHttpRequest is a reasonably clunky callback-based API, but it surely permits fine-grained management and, regardless of the identify, it’ll deal with responses in codecs aside from XML — corresponding to textual content, binary, JSON, and HTML.

Browsers have carried out the Fetch API from 2015. It’s an easier, simpler, extra constant, promise-based various to XMLHttpRequest.

Your server-side code can also need to make HTTP requests — sometimes to name APIs on different servers. From their first launch, each the Deno and Bun runtimes usefully replicated the browser’s Fetch API in order that comparable code might run on each the shopper and server. Node.js required a third-party module corresponding to node-fetch or axios till February 2022, when model 18 added the usual Fetch API. It’s nonetheless thought of experimental, however now you can use fetch() in every single place with equivalent code most often.

A Fundamental Fetch Instance

This easy instance fetches response information from a URI:

const response = await fetch('https://instance.com/information.json');

The fetch() name returns a promise which resolves with a Response object offering details about the end result. You’ll be able to parse the HTTP response physique right into a JavaScript object utilizing the promise-based .json() methodology:

const information = await response.json();

Consumer-side vs Server-side Fetch

The API could also be equivalent throughout platforms, however browsers implement restrictions when making client-side fetch() requests:

• Cross-origin useful resource sharing (CORS)

  Consumer-side JavaScript can solely talk with API endpoints inside its personal area. A script loaded from https://domainA.com/js/important.js can name any service at https://domainA.com/, corresponding to https://domainA.com/api/ or https://domainA.com/information/.

  It’s unimaginable to name a service on https://domainB.com/ — until that server permits entry by setting an HTTP Entry-Management-Enable-Origin header.

• Content material Safety Coverage (CSP)

  Your web pages/apps can set a Content material-Safety-Coverage HTTP header or meta tag to regulate permitted belongings in a web page. It may stop unintended or malicious injection of scripts, iframes, fonts, photographs, movies, and so forth. For instance, setting default-src 'self' stops fetch() requesting information exterior its personal area (XMLHttpRequest, WebSocket, server-sent occasions, and beacons are additionally restricted).

Server-side Fetch API calls in Node.js, Deno, and Bun have fewer restrictions, and you may request information from any server. That mentioned, third-party APIs could:

• require some type of authentication or authorization utilizing keys or OAuth
• have most request thresholds, corresponding to no multiple name per minute, or
• make a business cost for entry

You should utilize server-side fetch() calls to proxy client-side requests so you possibly can keep away from CORS and CSP points. That mentioned, keep in mind to be a conscientious net citizen and don’t bombard companies with 1000’s of requests that would take them down!

Customized Fetch Requests

The instance above requests information from the URI https://instance.com/information.json. Beneath the floor, JavaScript creates a Request object, which represents the complete particulars of that request corresponding to the strategy, headers, physique, and extra.

fetch() accepts two arguments:

• the useful resource – a string or URL object, and
• an optionally available choices parameter with additional request settings

For instance:

const response = await fetch('https://instance.com/information.json', {
   methodology: 'GET',
   credentials: 'omit',
   redirect: 'error',
   precedence: 'excessive'
});

The choices object can set following properties in Node.js or client-side code:

Optionally, you possibly can create a Request object and cross it to fetch(). This can be sensible should you can outline API endpoints upfront or need to ship a sequence comparable requests:

const request = new Request('https://instance.com/api/', {
  methodology: 'POST',
  physique: '{"a": 1, "b": 2, "c": 3}',
  credentials: 'omit'
});

console.log(`fetching ${ request.url }`);
const response = await fetch(request);

Dealing with HTTP Headers

You’ll be able to manipulate and look at HTTP headers within the request and response utilizing a Headers object. The API might be acquainted should you’ve used JavaScript Maps:

const headers = new Headers({
  'Content material-Sort': 'textual content/plain',
});


headers.append('Authorization', 'Fundamental abc123');


headers.set('Content material-Sort', 'utility/json');


const kind = headers.get('Content material-Sort');


if (headers.has('Authorization')) {

   
   headers.delete('Authorization');

}


headers.forEach((worth, identify) => {
  console.log(`${ identify }: ${ worth }`);
});


const response = await fetch('https://instance.com/information.json', {
   methodology: 'GET',
   headers
});


response.headers.forEach((worth, identify) => {
  console.log(`${ identify }: ${ worth }`);
});

Fetch Promise Resolve and Reject

You may presume a fetch() promise will reject when an endpoint returns a 404 Not Discovered or comparable server error. It doesn’t! The promise will resolve, as a result of that decision was profitable — even when the end result wasn’t what you anticipated.

A fetch() promise solely rejects when:

• you make an invalid request — corresponding to fetch('httttps://!invalidURL/');
• you abort the fetch() request, or
• there’s a community error, corresponding to a connection failure

Analyzing Fetch Responses

Profitable fetch() calls return a Response object containing details about the state and returned information. The properties are:

The next Response object strategies all return a promise, so it’s best to use await or .then blocks:

const response = await fetch('https://instance.com/information.json');


if ( response.okay && response.headers.get('Content material-Sort') === 'utility/json') {

   
   const obj = await response.json();

}

Aborting Fetch Requests

Node.js gained’t trip a fetch() request; it might run endlessly! Browsers can even wait between one and 5 minutes. It is best to abort fetch() underneath regular circumstances the place you’re anticipating a fairly fast response.

The next instance makes use of an AbortController object, which passes a sign property to the second fetch() parameter. A timeout runs the .abort() methodology if fetch doesn’t full inside 5 seconds:

const
  controller = new AbortController(),
  sign = controller.sign,
  timeout = setTimeout(() => controller.abort(), 5000);

strive {

  const response = await fetch('https://instance.com/slowrequest/', { sign });

  clearTimeout(timeout);

  console.log( response.okay );

}
catch (err) {

  
  console.log(err);

}

Node.js, Deno, Bun, and most browsers launched since mid-2022 additionally assist AbortSignal. This gives an easier timeout() methodology so that you don’t must handle your individual timers:

strive {

  
  const response = await fetch('https://instance.com/slowrequest/', {
    sign: AbortSignal.timeout( 5000 ),
  });

  console.log( response.okay );

}
catch (err) {

  
  console.log(err);

}

Efficient Fetches

Like every asynchronous, promise-based operation, it’s best to solely make fetch() calls in sequence when the enter of a name will depend on the output of a earlier one. The next code doesn’t carry out in addition to it might as a result of every API name should look ahead to the earlier one to resolve or reject. If every response takes one second, it’ll take a complete of three seconds to finish:

const response1 = await fetch('https://example1.com/api/');
const response2 = await fetch('https://example2.com/api/');
const response3 = await fetch('https://example3.com/api/');

The Promise.allSettled() methodology runs guarantees concurrently and fulfills when all have resolved or rejected. This code completes on the velocity of the slowest response. Will probably be 3 times sooner:

const information = await Promise.allSettled(
  [
    'https://example1.com/api/',
    'https://example2.com/api/',
    'https://example3.com/api/'
  ].map(url => fetch( url ))
);

information returns an array of objects the place:

• every has a standing property string of "fullfilled" or "rejected"
• if resolved, a worth property returns the fetch() response
• if rejected, a motive property returns the error

Abstract

Until you’re utilizing a legacy model of Node.js (17 or under), the Fetch API is accessible in JavaScript on each the server and shopper. It’s versatile, simple to make use of, and constant throughout all runtimes. A 3rd-party module ought to solely be needed should you require extra superior performance corresponding to caching, retries, or file dealing with.