JarCastingnode-fetch
A light-weight module that brings window.fetch to Node.js
(We are looking for v2 maintainers and collaborators)
- Motivation
- Features
- Difference from client-side fetch
- Installation
- Loading and configuring the module
- Common Usage
- Advanced Usage
- API
- License
- Acknowledgement
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.fetchAPI. - 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()andres.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.fetchoffers, 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));
Request cancellation with AbortSignal
NOTE: You may only cancel streamed requests on Node >= v8.0.0
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 follows:
import AbortController from 'abort-controller';
const controller = new AbortController();
const timeout = 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);
});
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
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, allows custom proxy, certificate, dns lookup 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) |
Transfer-Encoding |
chunked (when req.body is a stream) |
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:
typedestinationreferrerreferrerPolicymodecredentialscacheintegritykeepalive
The following node-fetch extension properties are provided:
followcompresscounteragent
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()typeredirectedtrailer
new Response([body[, options]])
(spec-compliant)
bodyA string or Readable streamoptionsAResponseInitoptions 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.
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 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
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.
(This API requires an optional dependency on npm package encoding, which you need to install manually. webpack users may see a warning message due to this optional dependency.)
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.
Acknowledgement
Thanks to github/fetch for providing a solid implementation reference.
node-fetch v1 was maintained by @bitinn, v2 is currently maintained by @TimothyGu, v2 readme is written by @jkantr.
License
MIT