A polyfill for fetch() that uses XMLHttpRequest
npm install fetchmeThis is forked from Github's excellent fetch polyfill. The difference is that this version doesn't touch any globals.
We use this with fetch-pretender for testing our UI and the data fetching logic therein.
The original readme follows:
This project adheres to the [Open Code of Conduct][code-of-conduct]. By participating, you are expected to uphold this code.
[code-of-conduct]: http://todogroup.org/opencodeofconduct/#fetch/opensource@github.com
The global fetch function is an easier way to make web requests and handle
responses than using an XMLHttpRequest. This polyfill is written as closely as
possible to the standard Fetch specification at https://fetch.spec.whatwg.org.
Available on Bower as fetch.
``sh`
$ bower install fetch
You'll also need a Promise polyfill for older browsers.
`sh`
$ bower install es6-promise
This can also be installed with npm.
`sh`
$ npm install whatwg-fetch --save
For a node.js implementation, try node-fetch.
For use with webpack, refer to Using WebPack with shims and polyfills.
For babel and es2015+, make sure to import the file:
`javascript`
import 'whatwg-fetch';
fetch(...);
The fetch function supports any HTTP method. We'll focus on GET and POST
example requests.
`javascript`
fetch('/users.html')
.then(function(response) {
return response.text()
}).then(function(body) {
document.body.innerHTML = body
})
`javascript`
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)
})
`javascript`
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)
})
`javascript
var form = document.querySelector('form')
fetch('/users', {
method: 'POST',
body: new FormData(form)
})
`
`javascript`
fetch('/users', {
method: 'POST',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
body: JSON.stringify({
name: 'Hubot',
login: 'hubot',
})
})
`javascript
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 a 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 any cookies to the server, resulting in
unauthenticated requests if the site relies on maintaining a user session.
#### Handling HTTP error statuses
To have fetch Promise reject on HTTP error statuses, i.e. on any non-2xx
status, define a custom response handler:
`javascript
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)
})
`
#### Sending cookies
To automatically send cookies for the current domain, the credentials option
must be provided:
`javascript`
fetch('/users', {
credentials: 'same-origin'
})
This option makes fetch behave similar to XMLHttpRequest with regards to
cookies. Otherwise, cookies won't get sent, resulting in these requests not
preserving the authentication session.
Use the include value to send cookies in a cross-origin resource sharing (CORS) request.
`javascript`
fetch('https://example.com:1234/users', {
credentials: 'include'
})
#### Receiving cookies
Like with XMLHttpRequest, the Set-Cookie response header returned from theresponse.headers.get()
server is a [forbidden header name][] and therefore can't be programatically
read with . Instead, it's the browser's responsibilitydocument.cookie
to handle new cookies being set (if applicable to the current URL). Unless they
are HTTP-only, new cookies will be available through .
[forbidden header name]: https://developer.mozilla.org/en-US/docs/Glossary/Forbidden_header_name
#### Obtaining the Response URL
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`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.
!Chrome | !Firefox | !IE | !Opera | !Safari
--- | --- | --- | --- | --- |
Latest ✔ | Latest ✔ | 10+ ✔ | Latest ✔ | 6.1+ ✔ |