How read excel file from file cabinet

i can read CSV file properly
but getting different format when trying to read excel file

i have tried following source code
{
//excel file read - showing incorrect format
var fileObj = nlapiLoadFile(4452);     
var fileName = fileObj.getName();      
var filedValue = fileObj.getValue();    
var decodeFile = decode_base64(filedValue);    


//CSV file read - showing proper format
var fileObj = nlapiLoadFile(4453);     
var fileName = fileObj.getName();      
var filedValue = fileObj.getValue();    
var decodeFile = decode_base64(filedValue); 
}

function decode_base64(s){
    var e = {}, i, k, v = [], r = '', w = String.fromCharCode;
    var n = [[65, 91], [97, 123], [48, 58], [47, 48], [43, 44]];
   
    for (z in n) {
        for (i = n[z][0]; i < n[z][1]; i++) {
            v.push(w(i));