A light-weight module that brings window.fetch to Node.js
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* v2.x readme overhaul with additions discussed in #448

added "comments" (TODO link references) for changes suggested but not yet implemented for future discussion/prs
    clarified "native stream" to be "native Node streams"
    adjusted all uses of http to https to encourage secure protocol usage
    adjusted whatwg to proper case, WHATWG
    made code block tags consistent as `js` instead of `javascript`
    uppercased all method option values (post vs POST)
    added spec-compliant node to the `response.ok` api section

* fix left over cruft, inconsistent hierarchy
Latest commit 745a27c Sep 1, 2018

README.md

node-fetch

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

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 for details.
  • 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 (2.x)

$ npm install node-fetch --save

Loading and configuring the module

We suggest you load the module via require, pending the stabalizing of es modules in node:

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

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

const Bluebird = require('bluebird');

fetch.Promise = Bluebird;

Common Usage

NOTE: The documentation below is up-to-date with 2.x releases, see 1.x readme, changelog and 2.x upgrade guide for the differences.

Plain text or HTML

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

JSON

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

Simple Post

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 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 in Node.js as of v7.5.0. 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 { URLSearchParams } = require('url');

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.

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:

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:

fetch('https://assets-cdn.github.com/images/modules/logos_page/Octocat.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 fileType = require('file-type');

fetch('https://assets-cdn.github.com/images/modules/logos_page/Octocat.png')
    .then(res => res.buffer())
    .then(buffer => fileType(buffer))
    .then(type => { /* ... */ });

Accessing Headers and other Meta data

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'));
    });

Post data using a file stream

const { createReadStream } = require('fs');

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

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

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

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

    // 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)
    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, allows custom proxy, certificate etc.
}
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)
User-Agent node-fetch/1.0 (+https://github.com/bitinn/node-fetch)

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

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
  • redirected
  • 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.

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 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)

The data 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 spec, 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.

body.textConverted()

(node-fetch extension)

  • Returns: Promise<String>

Identical to body.text(), except instead of always converting to UTF-8, encoding sniffing will be performed and text converted to UTF-8, if possible.

Class: FetchError

(node-fetch extension)

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

Acknowledgement

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

License

MIT