node-fetch
A light-weight module that brings window.fetch to node.js and io.js
Last updated 4 years ago by bitinn .
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Node Fetch

A light-weight module that brings window.fetch to Node.js.

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Motivation

Instead of implementing XMLHttpRequest in Node.js to run browser-specific Fetch polyfill, why not go from native http to fetch API directly? Hence, node-fetch, minimal code for a window.fetch compatible API on Node.js runtime.

See Matt Andrews' isomorphic-fetch or Leonardo Quixada's cross-fetch for isomorphic usage (exports node-fetch for server-side, whatwg-fetch for client-side).

Features

  • Stay consistent with window.fetch API.
  • Make conscious trade-off when following WHATWG fetch spec and stream spec implementation details, document known differences.
  • Use native promise, but allow substituting it with [insert your favorite promise library].
  • Use native Node streams for body, on both request and response.
  • Decode content encoding (gzip/deflate) properly, and convert string output (such as res.text() and res.json()) to UTF-8 automatically.
  • Useful extensions such as timeout, redirect limit, response size limit, explicit errors for troubleshooting.

Difference from client-side fetch

  • See known differences:
  • If you happen to use a missing feature that window.fetch offers, feel free to open an issue.
  • Pull requests are welcomed too!

Installation

Current stable release (3.x)

$ npm install node-fetch

Loading and configuring the module

// CommonJS
const fetch = require('node-fetch');

// ES Module
import fetch from 'node-fetch';

If you are using a Promise library other than native, set it through fetch.Promise:

const fetch = require('node-fetch');
const Bluebird = require('bluebird');

fetch.Promise = Bluebird;

If you want to patch the global object in node:

const fetch = require('node-fetch');

if (!globalThis.fetch) {
    globalThis.fetch = fetch;
}

For versions of node earlier than 12.x, use this globalThis polyfill:

(function() {
	if (typeof globalThis === 'object') return;
	Object.defineProperty(Object.prototype, '__magic__', {
		get: function() {
			return this;
		},
		configurable: true
	});
	__magic__.globalThis = __magic__;
	delete Object.prototype.__magic__;
}());

Upgrading

Using an old version of node-fetch? Check out the following files:

Common Usage

NOTE: The documentation below is up-to-date with 3.x releases, if you are using an older version, please check how to upgrade.

Plain text or HTML

const fetch = require('node-fetch');

fetch('https://github.com/')
	.then(res => res.text())
	.then(body => console.log(body));

JSON

const fetch = require('node-fetch');

fetch('https://api.github.com/users/github')
	.then(res => res.json())
	.then(json => console.log(json));

Simple Post

const fetch = require('node-fetch');

fetch('https://httpbin.org/post', {method: 'POST', body: 'a=1'})
	.then(res => res.json()) // expecting a json response
	.then(json => console.log(json));

Post with JSON

const fetch = require('node-fetch');

const body = {a: 1};

fetch('https://httpbin.org/post', {
	method: 'post',
	body: JSON.stringify(body),
	headers: {'Content-Type': 'application/json'}
})
	.then(res => res.json())
	.then(json => console.log(json));

Post with form parameters

URLSearchParams is available on the global object in Node.js as of v10.0.0. See official documentation for more usage methods.

NOTE: The Content-Type header is only set automatically to x-www-form-urlencoded when an instance of URLSearchParams is given as such:

const fetch = require('node-fetch');

const params = new URLSearchParams();
params.append('a', 1);

fetch('https://httpbin.org/post', {method: 'POST', body: params})
	.then(res => res.json())
	.then(json => console.log(json));

Handling exceptions

NOTE: 3xx-5xx responses are NOT exceptions, and should be handled in then(), see the next section.

Adding a catch to the fetch promise chain will catch all exceptions, such as errors originating from node core libraries, like network errors, and operational errors which are instances of FetchError. See the error handling document for more details.

const fetch = require('node-fetch');

fetch('https://domain.invalid/').catch(err => console.error(err));

Handling client and server errors

It is common to create a helper function to check that the response contains no client (4xx) or server (5xx) error responses:

const fetch = require('node-fetch');

function checkStatus(res) {
	if (res.ok) {
		// res.status >= 200 && res.status < 300
		return res;
	} else {
		throw MyCustomError(res.statusText);
	}
}

fetch('https://httpbin.org/status/400')
	.then(checkStatus)
	.then(res => console.log('will not get here...'));

Advanced Usage

Streams

The "Node.js way" is to use streams when possible:

const {createWriteStream} = require('fs');
const fetch = require('node-fetch');

fetch(
	'https://octodex.github.com/images/Fintechtocat.png'
).then(res => {
	const dest = fs.createWriteStream('./octocat.png');
	res.body.pipe(dest);
});

Buffer

If you prefer to cache binary data in full, use buffer(). (NOTE: buffer() is a node-fetch only API)

const fetch = require('node-fetch');
const fileType = require('file-type');

fetch('https://octodex.github.com/images/Fintechtocat.png')
	.then(res => res.buffer())
	.then(buffer => fileType(buffer))
	.then(type => {
		console.log(type);
	});

Accessing Headers and other Meta data

const fetch = require('node-fetch');

fetch('https://github.com/').then(res => {
	console.log(res.ok);
	console.log(res.status);
	console.log(res.statusText);
	console.log(res.headers.raw());
	console.log(res.headers.get('content-type'));
});

Extract Set-Cookie Header

Unlike browsers, you can access raw Set-Cookie headers manually using Headers.raw(). This is a node-fetch only API.

const fetch = require('node-fetch');

fetch('https://example.com').then(res => {
	// returns an array of values, instead of a string of comma-separated values
	console.log(res.headers.raw()['set-cookie']);
});

Post data using a file stream

const {createReadStream} = require('fs');
const fetch = require('node-fetch');

const stream = createReadStream('input.txt');

fetch('https://httpbin.org/post', {method: 'POST', body: stream})
	.then(res => res.json())
	.then(json => console.log(json));

Post with form-data (detect multipart)

const fetch = require('node-fetch');
const FormData = require('form-data');

const form = new FormData();
form.append('a', 1);

fetch('https://httpbin.org/post', {method: 'POST', body: form})
	.then(res => res.json())
	.then(json => console.log(json));

// OR, using custom headers
// NOTE: getHeaders() is non-standard API

const options = {
	method: 'POST',
	body: form,
	headers: form.getHeaders()
};

fetch('https://httpbin.org/post', options)
	.then(res => res.json())
	.then(json => console.log(json));

Request cancellation with AbortSignal

You may cancel requests with AbortController. A suggested implementation is abort-controller.

An example of timing out a request after 150ms could be achieved as the following:

const fetch = require('node-fetch');
const AbortController = require('abort-controller');

const controller = new AbortController();
const timeout = setTimeout(() => {
	controller.abort();
}, 150);

fetch('https://example.com', {signal: controller.signal})
	.then(res => res.json())
	.then(
		data => {
			useData(data);
		},
		err => {
			if (err.name === 'AbortError') {
                console.log('request was aborted');
			}
		}
	)
	.finally(() => {
		clearTimeout(timeout);
	});

See test cases for more examples.

API

fetch(url[, options])

  • url A string representing the URL for fetching
  • options Options for the HTTP(S) request
  • Returns: Promise<Response>

Perform an HTTP(S) fetch.

url should be an absolute url, such as https://example.com/. A path-relative URL (/file/under/root) or protocol-relative URL (//can-be-http-or-https.com/) will result in a rejected Promise.

Options

The default values are shown after each option key.

{
    // These properties are part of the Fetch Standard
    method: 'GET',
    headers: {},            // request headers. format is the identical to that accepted by the Headers constructor (see below)
    body: null,             // request body. can be null, a string, a Buffer, a Blob, or a Node.js Readable stream
    redirect: 'follow',     // set to `manual` to extract redirect headers, `error` to reject redirect
    signal: null,           // pass an instance of AbortSignal to optionally abort requests

    // The following properties are node-fetch extensions
    follow: 20,             // maximum redirect count. 0 to not follow redirect
    timeout: 0,             // req/res timeout in ms, it resets on redirect. 0 to disable (OS limit applies). Signal is recommended instead.
    compress: true,         // support gzip/deflate content encoding. false to disable
    size: 0,                // maximum response body size in bytes. 0 to disable
    agent: null,            // http(s).Agent instance or function that returns an instance (see below)
    highWaterMark: 16384    // the maximum number of bytes to store in the internal buffer before ceasing to read from the underlying resource.
}

Default Headers

If no values are set, the following request headers will be sent automatically:

Header Value
Accept-Encoding gzip,deflate (when options.compress === true)
Accept */*
Connection close (when no options.agent is present)
Content-Length (automatically calculated, if possible)
Transfer-Encoding chunked (when req.body is a stream)
User-Agent node-fetch (+https://github.com/node-fetch/node-fetch)

Note: when body is a Stream, Content-Length is not set automatically.

Custom Agent

The agent option allows you to specify networking related options which are out of the scope of Fetch, including and not limited to the following:

  • Support self-signed certificate
  • Use only IPv4 or IPv6
  • Custom DNS Lookup

See http.Agent for more information.

In addition, the agent option accepts a function that returns http(s).Agent instance given current URL, this is useful during a redirection chain across HTTP and HTTPS protocol.

const http = require('http');
const https = require('https');

const httpAgent = new http.Agent({
	keepAlive: true
});
const httpsAgent = new https.Agent({
	keepAlive: true
});

const options = {
	agent: function(_parsedURL) {
		if (_parsedURL.protocol == 'http:') {
			return httpAgent;
		} else {
			return httpsAgent;
		}
	}
};

Custom highWaterMark

Stream on Node.js have a smaller internal buffer size (16Kb, aka highWaterMark) from client-side browsers (>1Mb, not consistent across browsers). Because of that, when you are writing an isomorphic app and using res.clone(), it will hang with large response in Node.

The recommended way to fix this problem is to resolve cloned response in parallel:

const fetch = require('node-fetch');

fetch('https://example.com').then(res => {
	const r1 = res.clone();

	return Promise.all([res.json(), r1.text()]).then(results => {
		console.log(results[0]);
		console.log(results[1]);
	});
});

If for some reason you don't like the solution above, since 3.x you are able to modify the highWaterMark option:

const fetch = require('node-fetch');

fetch('https://example.com', {highWaterMark: 10}).then(res => res.clone().buffer());

Class: Request

An HTTP(S) request containing information about URL, method, headers, and the body. This class implements the Body interface.

Due to the nature of Node.js, the following properties are not implemented at this moment:

  • type
  • destination
  • referrer
  • referrerPolicy
  • mode
  • credentials
  • cache
  • integrity
  • keepalive

The following node-fetch extension properties are provided:

  • follow
  • compress
  • counter
  • agent
  • highWaterMark

See options for exact meaning of these extensions.

new Request(input[, options])

(spec-compliant)

  • input A string representing a URL, or another Request (which will be cloned)
  • options [Options][#fetch-options] for the HTTP(S) request

Constructs a new Request object. The constructor is identical to that in the browser.

In most cases, directly fetch(url, options) is simpler than creating a Request object.

Class: Response

An HTTP(S) response. This class implements the Body interface.

The following properties are not implemented in node-fetch at this moment:

  • Response.error()
  • Response.redirect()
  • type
  • trailer

new Response([body[, options]])

(spec-compliant)

Constructs a new Response object. The constructor is identical to that in the browser.

Because Node.js does not implement service workers (for which this class was designed), one rarely has to construct a Response directly.

response.ok

(spec-compliant)

Convenience property representing if the request ended normally. Will evaluate to true if the response status was greater than or equal to 200 but smaller than 300.

response.redirected

(spec-compliant)

Convenience property representing if the request has been redirected at least once. Will evaluate to true if the internal redirect counter is greater than 0.

Class: Headers

This class allows manipulating and iterating over a set of HTTP headers. All methods specified in the Fetch Standard are implemented.

new Headers([init])

(spec-compliant)

  • init Optional argument to pre-fill the Headers object

Construct a new Headers object. init can be either null, a Headers object, an key-value map object or any iterable object.

// Example adapted from https://fetch.spec.whatwg.org/#example-headers-class
const Headers = require('node-fetch');

const meta = {
	'Content-Type': 'text/xml',
	'Breaking-Bad': '<3'
};
const headers = new Headers(meta);

// The above is equivalent to
const meta = [['Content-Type', 'text/xml'], ['Breaking-Bad', '<3']];
const headers = new Headers(meta);

// You can in fact use any iterable objects, like a Map or even another Headers
const meta = new Map();
meta.set('Content-Type', 'text/xml');
meta.set('Breaking-Bad', '<3');
const headers = new Headers(meta);
const copyOfHeaders = new Headers(headers);

Interface: Body

Body is an abstract interface with methods that are applicable to both Request and Response classes.

The following methods are not yet implemented in node-fetch at this moment:

  • formData()

body.body

(deviation from spec)

Data are encapsulated in the Body object. Note that while the Fetch Standard requires the property to always be a WHATWG ReadableStream, in node-fetch it is a Node.js Readable stream.

body.bodyUsed

(spec-compliant)

  • Boolean

A boolean property for if this body has been consumed. Per the specs, a consumed body cannot be used again.

body.arrayBuffer()

body.blob()

body.json()

body.text()

(spec-compliant)

  • Returns: Promise

Consume the body and return a promise that will resolve to one of these formats.

body.buffer()

(node-fetch extension)

  • Returns: Promise<Buffer>

Consume the body and return a promise that will resolve to a Buffer.

Class: FetchError

(node-fetch extension)

An operational error in the fetching process. See ERROR-HANDLING.md for more info.

Class: AbortError

(node-fetch extension)

An Error thrown when the request is aborted in response to an AbortSignal's abort event. It has a name property of AbortError. See ERROR-HANDLING.MD for more info.

TypeScript

Since 3.x types are bundled with node-fetch, so you don't need to install any additional packages.

For older versions please use the type definitions from DefinitelyTyped:

$ npm install --save-dev @types/node-fetch

Acknowledgement

Thanks to github/fetch for providing a solid implementation reference.

Team

David Frank Jimmy Wärting Antoni Kepinski Richie Bendall Gregor Martynus
David Frank Jimmy Wärting Antoni Kepinski Richie Bendall Gregor Martynus
Former

License

MIT

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