code: function fixdata(data) {
  		var o = '',
  			l = 0,
  			w = 10240;
  		for (; l < data.byteLength / w; ++l)
  			o += String.fromCharCode.apply(null, new Uint8Array(data.slice(l * w, l * w + w)));
  		o += String.fromCharCode.apply(null, new Uint8Array(data.slice(l * w)));
  		return o;
  	}
docs: see https://github.com/SheetJS/js-xlsx/blob/5ae6b1965bfe3764656a96f536b356cd1586fec7/README.md
  for example of using readAsArrayBuffer under `Parsing Workbooks`