window.fetch polyfill
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.
Installation
Available on Bower as fetch.
$ bower install fetchYou'll also need a Promise polyfill for older browsers.
$ bower install es6-promiseThis can also be installed with npm.
$ npm install whatwg-fetch --saveUsage
The fetch function supports any HTTP method. We'll focus on GET and POST
example requests.
HTML
fetch('/users.html')
.then(function(response) {
return response.text()
}).then(function(body) {
document.body.innerHTML = body
})JSON
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)
})Response metadata
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)
})Post form
var form = document.querySelector('form')
fetch('/query', {
method: 'post',
body: new FormData(form)
})Post JSON
fetch('/users', {
method: 'post',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
body: JSON.stringify({
name: 'Hubot',
login: 'hubot',
})
})File upload
var input = document.querySelector('input[type="file"]')
var form = new FormData()
form.append('file', input.files[0])
form.append('user', 'hubot')
fetch('/avatars', {
method: 'post',
body: form
})Success and error handlers
This causes fetch to behave like jQuery's $.ajax by rejecting the Promise
on HTTP failure status codes like 404, 500, etc. The response Promise is
resolved only on successful, 200 level, status codes.
function status(response) {
if (response.status >= 200 && response.status < 300) {
return Promise.resolve(response)
} else {
return Promise.reject(new Error(response.statusText))
}
}
function json(response) {
return response.json()
}
fetch('/users')
.then(status)
.then(json)
.then(function(json) {
console.log('request succeeded with json response', json)
}).catch(function(error) {
console.log('request failed', error)
})Response URL caveat
The Response object has a URL attribute for the final responded resource.
Usually this is the same as the Request url, but in the case of a redirect,
its all transparent. Newer versions of XHR include a responseURL attribute
that returns this value. But not every browser supports this. The compromise
requires setting a special server side header to tell the browser what URL it
just requested (yeah, I know browsers).
response.headers['X-Request-URL'] = request.urlIf you want response.url to be reliable, you'll want to set this header. The
day that you ditch this polyfill and use native fetch only, you can remove the
header hack.
Browser Support
 |
 |
 |
 |
 |
|---|---|---|---|---|
| Latest ✔ | Latest ✔ | 9+ ✔ | Latest ✔ | 6.1+ ✔ |
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent