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/[email protected]

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.

NOTE: This fork permits fetching local files (file://), which is often required when creating hybrid applications. In this instance, XHR's status is often returned as zero. When checking for success, the original version of this module will throw an error. This fork will treat the zero as an acceptable response.

This can be installed with npm.

$ npm install https://github.com/kerrishotts/fetch --save

For a node.js implementation, try node-fetch.

For use with webpack, refer to Using WebPack with shims and polyfills.

The fetch function supports any HTTP method. We'll focus on GET and POST example requests.

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: {
    'Accept': 'application/json',
    '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 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.

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'
})

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.

fetch('https://example.com:1234/users', {
  credentials: 'include'
})

Like with XMLHttpRequest, the Set-Cookie response header returned from the server is a forbidden header name and therefore can't be programatically 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.

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.

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