Javascript - The onreadystatechange event

Three important properties of the XMLHttpRequest object:


onreadystatechange: Stores a function (or the name of a function) to be called automatically each time the readyState property changes

 

readyState: Holds the status of the XMLHttpRequest. Changes from 0 to 4:

  • 0: request not initialized
  • 1: server connection established
  • 2: request received
  • 3: processing request
  • 4: request finished and response is ready


status:

  • 200: OK
  • 404: Page not found