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A light-weight module that bringswindow.fetch to Node.js

(We are looking forv2 maintainers and collaborators)

• Motivation
• Features
• Difference from client-side fetch
• Installation
• Loading and configuring the module
• Common Usage
  • Plain text or HTML
  • JSON
  • Simple Post
  • Post with JSON
  • Post with form parameters
  • Handling exceptions
  • Handling client and server errors
• Advanced Usage
  • Streams
  • Buffer
  • Accessing Headers and other Meta data
  • Extract Set-Cookie Header
  • Post data using a file stream
  • Post with form-data (detect multipart)
  • Request cancellation with AbortSignal
• API
  • fetch(url[, options])
  • Options
  • Class: Request
  • Class: Response
  • Class: Headers
  • Interface: Body
  • Class: FetchError
• License
• Acknowledgement

Instead of implementingXMLHttpRequest in Node.js to run browser-specificFetch polyfill, why not go from nativehttp tofetch API directly? Hence,node-fetch, minimal code for awindow.fetch compatible API on Node.js runtime.

See Matt Andrews'isomorphic-fetch or Leonardo Quixada'scross-fetch for isomorphic usage (exportsnode-fetch for server-side,whatwg-fetch for client-side).

• Stay consistent withwindow.fetch API.
• Make conscious trade-off when followingWHATWG fetch spec andstream 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 asres.text() andres.json()) to UTF-8 automatically.
• Useful extensions such as timeout, redirect limit, response size limit,explicit errors for troubleshooting.

• SeeKnown Differences for details.
• If you happen to use a missing feature thatwindow.fetch offers, feel free to open an issue.
• Pull requests are welcomed too!

Current stable release (2.x)

$ npm install node-fetch

We suggest you load the module viarequire until the stabilization of ES modules in node:

constfetch=require('node-fetch');

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

constBluebird=require('bluebird');fetch.Promise=Bluebird;

NOTE: The documentation below is up-to-date with2.x releases; see the1.x readme,changelog and2.x upgrade guide for the differences.

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

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

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

constbody={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));

URLSearchParams is available in Node.js as of v7.5.0. Seeofficial documentation for more usage methods.

NOTE: TheContent-Type header is only set automatically tox-www-form-urlencoded when an instance ofURLSearchParams is given as such:

const{ URLSearchParams}=require('url');constparams=newURLSearchParams();params.append('a',1);fetch('https://httpbin.org/post',{method:'POST',body:params}).then(res=>res.json()).then(json=>console.log(json));

NOTE: 3xx-5xx responses areNOT exceptions and should be handled inthen(); see the next section for more information.

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

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

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

functioncheckStatus(res){if(res.ok){// res.status >= 200 && res.status < 300returnres;}else{throwMyCustomError(res.statusText);}}fetch('https://httpbin.org/status/400').then(checkStatus).then(res=>console.log('will not get here...'))

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

fetch('https://assets-cdn.github.com/images/modules/logos_page/Octocat.png').then(res=>{constdest=fs.createWriteStream('./octocat.png');res.body.pipe(dest);});

In Node.js 14 you can also use async iterators to readbody; however, be careful to catcherrors -- the longer a response runs, the more likely it is to encounter an error.

constfetch=require('node-fetch');constresponse=awaitfetch('https://httpbin.org/stream/3');try{forawait(constchunkofresponse.body){console.dir(JSON.parse(chunk.toString()));}}catch(err){console.error(err.stack);}

In Node.js 12 you can also use async iterators to readbody; however, async iterators with streamsdid not mature until Node.js 14, so you need to do some extra work to ensure you handle errorsdirectly from the stream and wait on it response to fully close.

constfetch=require('node-fetch');constread=asyncbody=>{leterror;body.on('error',err=>{error=err;});forawait(constchunkofbody){console.dir(JSON.parse(chunk.toString()));}returnnewPromise((resolve,reject)=>{body.on('close',()=>{error ?reject(error) :resolve();});});};try{constresponse=awaitfetch('https://httpbin.org/stream/3');awaitread(response.body);}catch(err){console.error(err.stack);}

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

constfileType=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=>{/* ... */});

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'));});

Unlike browsers, you can access rawSet-Cookie headers manually usingHeaders.raw(). This is anode-fetch only API.

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

const{ createReadStream}=require('fs');conststream=createReadStream('input.txt');fetch('https://httpbin.org/post',{method:'POST',body:stream}).then(res=>res.json()).then(json=>console.log(json));

constFormData=require('form-data');constform=newFormData();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 APIconstform=newFormData();form.append('a',1);constoptions={method:'POST',body:form,headers:form.getHeaders()}fetch('https://httpbin.org/post',options).then(res=>res.json()).then(json=>console.log(json));

NOTE: You may cancel streamed requests only on Node >= v8.0.0

You may cancel requests withAbortController. A suggested implementation isabort-controller.

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

importAbortControllerfrom'abort-controller';constcontroller=newAbortController();consttimeout=setTimeout(()=>{controller.abort();},150,);fetch(url,{signal:controller.signal}).then(res=>res.json()).then(data=>{useData(data)},err=>{if(err.name==='AbortError'){// request was aborted}},).finally(()=>{clearTimeout(timeout);});

Seetest cases for more examples.

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

Perform an HTTP(S) fetch.

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

The default values are shown after each option key.

{// These properties are part of the Fetch Standardmethod:'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 streamredirect:'follow',// set to `manual` to extract redirect headers, `error` to reject redirectsignal:null,// pass an instance of AbortSignal to optionally abort requests// The following properties are node-fetch extensionsfollow:20,// maximum redirect count. 0 to not follow redirecttimeout: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 disablesize:0,// maximum response body size in bytes. 0 to disableagent:null// http(s).Agent instance or function that returns an instance (see below)}

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

Note: whenbody is aStream,Content-Length is not set automatically.

Theagent 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

Seehttp.Agent for more information.

If no agent is specified, the default agent provided by Node.js is used. Note thatthis changed in Node.js 19 to havekeepalive true by default. If you wish to enablekeepalive in an earlier version of Node.js, you can override the agent as per the following code sample.

In addition, theagent option accepts a function that returnshttp(s).Agent instance given currentURL, this is useful during a redirection chain across HTTP and HTTPS protocol.

consthttpAgent=newhttp.Agent({keepAlive:true});consthttpsAgent=newhttps.Agent({keepAlive:true});constoptions={agent:function(_parsedURL){if(_parsedURL.protocol=='http:'){returnhttpAgent;}else{returnhttpsAgent;}}}

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

Seeoptions for exact meaning of these extensions.

(spec-compliant)

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

Constructs a newRequest object. The constructor is identical to that in thebrowser.

In most cases, directlyfetch(url, options) is simpler than creating aRequest object.

An HTTP(S) response. This class implements theBody interface.

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

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

(spec-compliant)

• body AString orReadable stream
• options AResponseInit options dictionary

Constructs a newResponse object. The constructor is identical to that in thebrowser.

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

(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.

(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.

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

(spec-compliant)

• init Optional argument to pre-fill theHeaders object

Construct a newHeaders object.init can be eithernull, aHeaders object, an key-value map object or any iterable object.

// Example adapted from https://fetch.spec.whatwg.org/#example-headers-classconstmeta={'Content-Type':'text/xml','Breaking-Bad':'<3'};constheaders=newHeaders(meta);// The above is equivalent toconstmeta=[['Content-Type','text/xml'],['Breaking-Bad','<3']];constheaders=newHeaders(meta);// You can in fact use any iterable objects, like a Map or even another Headersconstmeta=newMap();meta.set('Content-Type','text/xml');meta.set('Breaking-Bad','<3');constheaders=newHeaders(meta);constcopyOfHeaders=newHeaders(headers);

Body is an abstract interface with methods that are applicable to bothRequest andResponse classes.

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

• formData()

(deviation from spec)

• Node.jsReadable stream

Data are encapsulated in theBody object. Note that while theFetch Standard requires the property to always be a WHATWGReadableStream, in node-fetch it is a Node.jsReadable stream.

(spec-compliant)

• Boolean

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

(spec-compliant)

• Returns:Promise

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

(node-fetch extension)

• Returns:Promise<Buffer>

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

(node-fetch extension)

• Returns:Promise<String>

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

(This API requires an optional dependency of the npm packageencoding, which you need to install manually.webpack users may seea warning message due to this optional dependency.)

(node-fetch extension)

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

(node-fetch extension)

An Error thrown when the request is aborted in response to anAbortSignal'sabort event. It has aname property ofAbortError. SeeERROR-HANDLING.MD for more info.

Thanks togithub/fetch for providing a solid implementation reference.

node-fetch v1 was maintained by@bitinn; v2 was maintained by@TimothyGu,@bitinn and@jimmywarting; v2 readme is written by@jkantr.

MIT