whatwg-fetch
Advanced tools
The whatwg-fetch npm package is a polyfill for the Fetch API, a modern interface for making network requests in browsers and Node.js. It allows developers to make HTTP requests to retrieve or send data to remote servers in an easy and efficient way. The Fetch API provides a more powerful and flexible feature set compared to older technologies like XMLHttpRequest.
Making GET requests
This code sample demonstrates how to make a GET request to retrieve data from a specified URL and then process the response as JSON.
fetch('https://api.example.com/data')
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error('Error:', error));Making POST requests
This code sample shows how to make a POST request to send JSON data to a server and then handle the JSON response.
fetch('https://api.example.com/data', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify({ key: 'value' })
})
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error('Error:', error));Handling HTTP errors
This code sample illustrates how to handle HTTP errors by checking the response status before processing the response.
fetch('https://api.example.com/data')
.then(response => {
if (!response.ok) {
throw new Error('Network response was not ok');
}
return response.json();
})
.then(data => console.log(data))
.catch(error => console.error('Error:', error));Axios is a popular HTTP client for the browser and Node.js. It provides a promise-based API and has a similar feature set to whatwg-fetch, including interceptors, automatic transforms for JSON data, and cancellation. Axios is often preferred for its more convenient error handling and wider browser support without polyfills.
node-fetch is a light-weight module that brings the Fetch API to Node.js. It is similar to whatwg-fetch but is specifically designed for Node.js environments. It provides a simple interface for making HTTP requests and is a drop-in replacement for native fetch in Node.js.
Ky is a tiny and elegant HTTP client based on the Fetch API. It extends the capabilities of fetch with additional features like retrying failed requests, timeout handling, and more convenient methods for parsing responses. Ky is designed to offer a more developer-friendly API compared to whatwg-fetch.
The fetch() function is a Promise-based mechanism for programmatically making
web requests in the browser. This project is a polyfill that implements a subset
of the standard Fetch specification, enough to make fetch a viable
replacement for most uses of XMLHttpRequest in traditional web applications.
This project adheres to the Open Code of Conduct. By participating, you are expected to uphold this code.
If you believe you found a bug with how fetch behaves in Chrome or Firefox,
please don't open an issue in this repository. This project is a
polyfill, and since Chrome and Firefox both implement the window.fetch
function natively, no code from this project actually takes any effect in
these browsers. See Browser support for detailed
information.
If you have trouble making a request to another domain (a different subdomain or port number also constitutes another domain), please familiarize yourself with all the intricacies and limitations of CORS requests. Because CORS requires participation of the server by implementing specific HTTP response headers, it is often nontrivial to set up or debug. CORS is exclusively handled by the browser's internal mechanisms which this polyfill cannot influence.
If you have trouble maintaining the user's session or CSRF protection
through fetch requests, please ensure that you've read and understood the
Sending cookies section. fetch doesn't send cookies
unless you ask it to.
This project doesn't work under Node.js environments. It's meant for web browsers only. You should ensure that your application doesn't try to package and run this on the server.
If you have an idea for a new feature of fetch, submit your feature
requests to the specification's repository.
We only add features and APIs that are part of the Fetch specification.
npm install whatwg-fetch --save; or
bower install fetch; or
yarn add whatwg-fetch.
You will also need a Promise polyfill for older browsers. We recommend taylorhakes/promise-polyfill for its small size and Promises/A+ compatibility.
For use with webpack, add this package in the entry configuration option
before your application entry point:
entry: ['whatwg-fetch', ...]
For Babel and ES2015+, make sure to import the file:
import 'whatwg-fetch'
For a more comprehensive API reference that this polyfill supports, refer to https://github.github.io/fetch/.
fetch('/users.html')
.then(function(response) {
return response.text()
}).then(function(body) {
document.body.innerHTML = body
})
fetch('/users.json')
.then(function(response) {
return response.json()
}).then(function(json) {
console.log('parsed json', json)
}).catch(function(ex) {
console.log('parsing failed', ex)
})
fetch('/users.json').then(function(response) {
console.log(response.headers.get('Content-Type'))
console.log(response.headers.get('Date'))
console.log(response.status)
console.log(response.statusText)
})
var form = document.querySelector('form')
fetch('/users', {
method: 'POST',
body: new FormData(form)
})
fetch('/users', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify({
name: 'Hubot',
login: 'hubot',
})
})
var input = document.querySelector('input[type="file"]')
var data = new FormData()
data.append('file', input.files[0])
data.append('user', 'hubot')
fetch('/avatars', {
method: 'POST',
body: data
})
The fetch specification differs from jQuery.ajax() in mainly two ways that
bear keeping in mind:
The Promise returned from fetch() won't reject on HTTP error status
even if the response is an HTTP 404 or 500. Instead, it will resolve normally,
and it will only reject on network failure or if anything prevented the
request from completing.
By default, fetch won't send or receive any cookies from the server,
resulting in unauthenticated requests if the site relies on maintaining a user
session. See Sending cookies for how to opt into cookie
handling.
To have fetch Promise reject on HTTP error statuses, i.e. on any non-2xx
status, define a custom response handler:
function checkStatus(response) {
if (response.status >= 200 && response.status < 300) {
return response
} else {
var error = new Error(response.statusText)
error.response = response
throw error
}
}
function parseJSON(response) {
return response.json()
}
fetch('/users')
.then(checkStatus)
.then(parseJSON)
.then(function(data) {
console.log('request succeeded with JSON response', data)
}).catch(function(error) {
console.log('request failed', error)
})
To automatically send cookies for the current domain, the credentials option
must be provided:
fetch('/users', {
credentials: 'same-origin'
})
The "same-origin" value makes fetch behave similarly to XMLHttpRequest with
regards to cookies. Otherwise, cookies won't get sent, resulting in these
requests not preserving the authentication session.
For CORS requests, use the "include" value to allow sending credentials to other domains:
fetch('https://example.com:1234/users', {
credentials: 'include'
})
As with XMLHttpRequest, the Set-Cookie response header returned from the
server is a forbidden header name and therefore can't be programmatically
read with response.headers.get(). Instead, it's the browser's responsibility
to handle new cookies being set (if applicable to the current URL). Unless they
are HTTP-only, new cookies will be available through document.cookie.
Bear in mind that the default behavior of fetch is to ignore the Set-Cookie
header completely. To opt into accepting cookies from the server, you must use
the credentials option.
Due to limitations of XMLHttpRequest, the response.url value might not be
reliable after HTTP redirects on older browsers.
The solution is to configure the server to set the response HTTP header
X-Request-URL to the current URL after any redirect that might have happened.
It should be safe to set it unconditionally.
# Ruby on Rails controller example
response.headers['X-Request-URL'] = request.url
This server workaround is necessary if you need reliable response.url in
Firefox < 32, Chrome < 37, Safari, or IE.
Note: modern browsers such as Chrome, Firefox, Microsoft Edge, and Safari contain native
implementations of window.fetch, therefore the code from this polyfill doesn't
have any effect on those browsers. If you believe you've encountered an error
with how window.fetch is implemented in any of these browsers, you should file
an issue with that browser vendor instead of this project.
29 March 2018
#604#553#534credentials: omit #526#492#496#469#49154dc3f80ecdd407831671FAQs
A window.fetch polyfill.
The npm package whatwg-fetch receives a total of 10,161,252 weekly downloads. As such, whatwg-fetch popularity was classified as popular.
We found that whatwg-fetch demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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