JarCasting
A light-weight module that brings Fetch API to Node.js.
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- Motivation
- Features
- Difference from client-side fetch
- Installation
- Loading and configuring the module
- Upgrading
- Common Usage
- Advanced Usage
- API
- TypeScript
- Acknowledgement
- Team - Former
- License
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 Jason Miller's isomorphic-unfetch 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.fetchAPI. - Make conscious trade-off when following WHATWG fetch spec and stream spec implementation details, document known differences.
- Use native promise and async functions.
- Use native Node streams for body, on both request and response.
- Decode content encoding (gzip/deflate/brotli) properly, and convert string output (such as
res.text()andres.json()) to UTF-8 automatically. - Useful extensions such as 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.fetchoffers, 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 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, use this globalThis polyfill.
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');
const response = await fetch('https://github.com/');
const body = await response.text();
console.log(body);
JSON
const fetch = require('node-fetch');
const response = await fetch('https://api.github.com/users/github');
const json = await response.json();
console.log(json);
Simple Post
const fetch = require('node-fetch');
const response = await fetch('https://httpbin.org/post', {method: 'POST', body: 'a=1'});
const json = await response.json();
console.log(json);
Post with JSON
const fetch = require('node-fetch');
const body = {a: 1};
const response = await fetch('https://httpbin.org/post', {
method: 'post',
body: JSON.stringify(body),
headers: {'Content-Type': 'application/json'}
});
const json = await response.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);
const response = await fetch('https://httpbin.org/post', {method: 'POST', body: params});
const json = await response.json();
console.log(json);
Handling exceptions
NOTE: 3xx-5xx responses are NOT exceptions, and should be handled in then(), see the next section.
Wrapping the fetch function into a try/catch block 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');
try {
await fetch('https://domain.invalid/');
} catch (error) {
console.log(error);
}
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');
class HTTPResponseError extends Error {
constructor(response, ...args) {
this.response = response;
super(`HTTP Error Response: ${res.status} ${res.statusText}`, ...args);
}
}
const checkStatus = response => {
if (response.ok) {
// response.status >= 200 && response.status < 300
return res;
} else {
throw new HTTPResponseError(response);
}
}
const response = await fetch('https://httpbin.org/status/400');
try {
checkStatus(response);
} catch (error) {
console.error(error);
const errorBody = await error.response.text();
console.error(`Error body: ${errorBody}`);
}
Handling cookies
Cookies are not stored by default. However, cookies can be extracted and passed by manipulating request and response headers. See Extract Set-Cookie Header for details.
Advanced Usage
Streams
The "Node.js way" is to use streams when possible. You can pipe res.body to another stream. This example uses stream.pipeline to attach stream error handlers and wait for the download to complete.
const {createWriteStream} = require('fs');
const {pipeline} = require('stream');
const {promisify} = require('util');
const fetch = require('node-fetch');
const streamPipeline = promisify(pipeline);
const response = await fetch('https://assets-cdn.github.com/images/modules/logos_page/Octocat.png');
if (!response.ok) throw new Error(`unexpected response ${response.statusText}`);
await streamPipeline(response.body, createWriteStream('./octocat.png'));
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');
const response = await fetch('https://octodex.github.com/images/Fintechtocat.png');
const buffer = await response.buffer();
const type = await fileType.fromBuffer(buffer)
console.log(type);
Accessing Headers and other Meta data
const fetch = require('node-fetch');
const response = await fetch('https://github.com/');
console.log(response.ok);
console.log(response.status);
console.log(response.statusText);
console.log(response.headers.raw());
console.log(response.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');
const response = await fetch('https://example.com');
// Returns an array of values, instead of a string of comma-separated values
console.log(response.headers.raw()['set-cookie']);
Post data using a file stream
const {createReadStream} = require('fs');
const fetch = require('node-fetch');
const stream = createReadStream('input.txt');
const response = await fetch('https://httpbin.org/post', {method: 'POST', body: stream});
const json = await response.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);
const response = await fetch('https://httpbin.org/post', {method: 'POST', body: form});
const json = await response.json();
console.log(json)
// OR, using custom headers
// NOTE: getHeaders() is non-standard API
const options = {
method: 'POST',
body: form,
headers: form.getHeaders()
};
const response = await fetch('https://httpbin.org/post', options);
const json = await response.json();
console.log(json)
node-fetch also supports spec-compliant FormData implementations such as formdata-node:
const fetch = require('node-fetch');
const FormData = require('form-data');
const form = new FormData();
form.set('greeting', 'Hello, world!');
const response = await fetch('https://httpbin.org/post', {method: 'POST', body: form});
const json = await response.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);
try {
const response = await fetch('https://example.com', {signal: controller.signal});
const data = await response.json();
} catch (error) {
if (error instanceof fetch.AbortError) {
console.log('request was aborted');
}
} finally {
clearTimeout(timeout);
}
See test cases for more examples.
API
fetch(url[, options])
urlA string representing the URL for fetchingoptionsOptions 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
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.
insecureHTTPParser: false // Use an insecure HTTP parser that accepts invalid HTTP headers when `true`.
}
Default Headers
If no values are set, the following request headers will be sent automatically:
| Header | Value |
|---|---|
Accept-Encoding |
gzip,deflate,br (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 |
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');
const response = await fetch('https://example.com');
const r1 = await response.clone();
const results = await Promise.all([response.json(), r1.text()]);
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');
const response = await fetch('https://example.com', {
// About 1MB
highWaterMark: 1024 * 1024
});
const result = await res.clone().buffer();
console.dir(result);
Insecure HTTP Parser
Passed through to the insecureHTTPParser option on http(s).request. See http.request for more information.
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:
typedestinationreferrerreferrerPolicymodecredentialscacheintegritykeepalive
The following node-fetch extension properties are provided:
followcompresscounteragenthighWaterMark
See options for exact meaning of these extensions.
new Request(input[, options])
(spec-compliant)
inputA string representing a URL, or anotherRequest(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()typetrailer
new Response([body[, options]])
(spec-compliant)
bodyAStringorReadablestreamoptionsAResponseInitoptions dictionary
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)
initOptional argument to pre-fill theHeadersobject
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)
- Node.js
Readablestream
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 |