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Client is a function that is responsible for communication with the server. The default client is used to communicate with the REST server. However, there is nothing to prevent us from changing and creating the client we need. Thanks to event communication, we can set our own client as we wish.

By default, the client is responsible for requests, but its role is very significant for many other elements - such as tracking the progress of requests, listening for cancellation, mapping payload and headers. It also applies all the interceptors in requesting lifecycle.


If there is no XHR in the window object or the XHR object is a polyfill in your environment, you have to install a npm package xmlhttprequest and set it on the window object.


fetchClient(command, requestId)


  • Requests handler of the builder dispatchers
  • Changeability of the handler to provide more flexibility