The onreadystatechange Event

• Defines the function to be called when the readyState Property changes

AJAX>XMLHttpRequest.onreadystatechange

https://www.w3schools.com/tags/ref_httpmessages.asp

This is just a few of the more popular Status messages for all of them you can visit:

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