FileReader
  event handlers:
    onloadstart
		onprogress
		onloadend : failure or success
		onload : on success, (evt) => { evt.target.result is the data }
		onabort
		onerror
	methods
		abort
		readAsArrayBuffer : result will be ArrayBuffer
		readAsBinaryString : result will be binary data as string
		readAsDataURL : result will be data: URL
		readAsText : result will be content as string