The responseType property of the XMLHttpRequest object can be set to change the expected response type from the server. Possible values are the empty string (default), "arraybuffer", "blob", "document", "json", and "text". The response property will contain the entity body according to responseType, as an ArrayBuffer, Blob, Document, JSON, or string. This is null if the request is not complete or was not successful.

AJAX FileReader MIME XMLHttpRequest

The FileReader.onload property contains a event handler executed when the load event is fired, when content read with readAsArrayBuffer, readAsBinaryString, readAsDataURL or readAsText is available.

Event Handler File FileReader Property Reference

The FileReader interface's readAsArrayBuffer() method is used to start reading the contents of a specified Blob or File. When the read operation is finished, the readyState becomes DONE, and the loadend is triggered. At that time, the result attribute contains an ArrayBuffer representing the file's data.

API DOM File API FileReader Files Method readAsArrayBuffer Reference