When a request to a server is sent, we want to perform some actions based on the response.
The onreadystatechange event is triggered every time the readyState changes.
The readyState property holds the status of the XMLHttpRequest.
Three important properties of the XMLHttpRequest object:
In the onreadystatechange event, we specify what will happen when the server response is ready to
When readyState is 4 and status is 200, the response is ready:
Note: The onreadystatechange event is triggered four times, one time for each change in
A callback function is a function passed as a parameter to another function.
If you have more than one AJAX task on your website, you should create ONE standard function for
creating the XMLHttpRequest object, and call this for each AJAX task.
The function call should contain the URL and what to do on onreadystatechange (which is probably
different for each call):
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