The XMLHttpRequestEventTarget.onabort is the function called when an XMLHttpRequest transaction is aborted, such as when the XMLHttpRequest.abort() function is called.
Syntax
XMLHttpRequest.onabort = callback;
Values
callback is the function to be executed when the transaction is aborted.
Example
var xmlhttp = new XMLHttpRequest(),
method = 'GET',
url = 'https://developer.mozilla.org/';
xmlhttp.open(method, url, true);
xmlhttp.onabort = function () {
console.log('** The request was aborted');
};
xmlhttp.send();
//..
xmlhttp.abort(); // This will invoke our onabort handler above