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A tiny wrapper around XMLHttpRequest.

Browser support

It is tested in the following browsers:

  • Chrome v. 23
  • Firefox v. 17
  • Opera v. 12.11
  • Safari v. 6
  • IE v. 9
  • IE v. 8

It requires an ES6 compatible Promise implementation. You can shim this with either es6-shim or es6-promise. The Promise constructor should be available in global scope.

Note for IE8 and below: You need to supply a shim for Function.prototype.bind.

It does not work in IE7 or below out of the box when receiving application/json, because JSON.parse is not supported. If this is a requirement, then use something like json2 from Douglas Crockford. Everything else seems to work.


Using this could not be more simple:

var fajax = require('fajax')
    baseUrl: '',
    accept: 'application/json'
fajax.get('/some-resource').then(function(xhr) {
    // if the server returns Content-Type: application/json,
    // this is already parsed for us
    var jsonBody = xhr.body

// Sometime later'/some-action', { json: jsonBody })
    .then(function(xhr) {
        // Report success
    // The promise is rejected if the status code is 400 or higher
    function(xhr) {
        // Handle validation error or the like


Include this by calling var fajax = require('fajax'). This require that you use a build-tool that is compatible with CommonJS, such as browserify or webpack.

The returned function have two static methods:

  1. fajax.qs(queryStringCreator): Assigns a specific query-string creator function. This is used when form is specified in the options.

    For example, it is simple to use the excellent qs library:

    // fajax and qs loaded via ender:
  2. fajax.defaults(newDefaults): Updates the defaults. Notice that this adds to the defaults, so

    fajax.defaults({ method: 'post' });
    fajax.defaults({ accept: 'application/json' })

    is the same as

    { method: 'post'
    , accept: 'application/json'

An interesting parameter in the defaults is baseUrl. This is resolved on the url passed in when initiating a request, so this is an easy way to normalize urls based on either a folder or a server.

fajax.defaults({ baseUrl: '' })
fajax.get('/test') // -> GET to

fajax.defaults({ baseUrl: '/foo' })
fajax.get('bar') // -> GET to <currentDomain>/foo/bar
fajax.get('/absolute') // -> GET to <currentDomain>/absolute

The function itself can take 3 arguments:

  1. An options dictionary (more on this below).
  2. A string of the url for the request. This can also be given as url in the options dictionary.
  3. An optional function that will be called when the request is complete. This can also be given as onload in the options dictionary.

The options dictionary supports the following keys:

  • headers: A key-value based list of request headers to set.

  • accept: The accept header. This defaults to the browsers normal value. If accept is set here, it will override the value in the headers-list.

  • method: The http-method to use. It defaults to GET.

  • body: Sends some text to the server. It defaults the Content-Type header to text/plain, but won't override a specifically set header.

  • json: Sends the given object as JSON. This requires JSON.stringify to be available in global scope.

    It will override Content-Type with application/json.

  • form: Sends the given string or object as form-parameters. The basic implementation will only send a flat object, discarding any values that are not String, Boolean or Number.

    For a more extensive implementation, you can provide any function via the fajax.qs(func) function.

    It will override Content-Type with application/x-www-form-urlencoded.

It is also possible to initiate a request with fajax.request(). It takes the method as the first parameter, but otherwise acts exactly like fajax().

For convenience, there are shorthands for the basic HTTP methods:

  • fajax.get()
  • fajax.head()
  • fajax.put()
  • fajax.delete() or fajax.del()
  • fajax.patch()
  • fajax.options()

They all act as the primary function (fajax()), except they also enforce the method option.