How do I detect requests initiated by the new fetch standard? How should I detect an AJAX request in general?

Question

On a server it can be useful to know that an incoming request is AJAX.

Most js libraries use XMLHttpRequest and so provide HTTP_X_REQUESTED_WITH: XMLHttpRequest, but neither Chrome's implementation nor Github's polyfill of the new fetch uses a similar header. So how can one detect that the request is AJAX?

Why is a request identifying its initiator not enforced through standards for fetch and XMLHttpRequest? Should something else be used for decision-making (e.g. clients providing the content-type they expect in response)?

Answer 1

Check out this issue on the Github's polyfill repository, specially this comment.

Since the X-Requested-With header is not an standard, they are using a wrapper that provides some of the missing behavior.

If you need more guidance, check this lines of the wrapper code:

function headers(options) {
  options = options || {}
  options.headers = options.headers || {}
  options.headers['X-Requested-With'] = 'XMLHttpRequest'
  return options
}