The XMLHttpRequestEventTarget.onerror is the function called when an XMLHttpRequest transaction fails due to an error.
The XMLHttpRequestEventTarget.onload is the function called when an XMLHttpRequest transaction completes successfully.
The XMLHttpRequestEventTarget.onloadstart is the function called when an XMLHttpRequest transaction starts transferring data.
The XMLHttpRequestEventTarget.onprogress is the function called periodically with information when an XMLHttpRequest before success completely .