How to interpret on what JQuery do?

How to interpret on what JQuery do?

Referring to following coding , I would like to know on how to interpret following coding as show below:

//export
that._eTTE('equity_future_export','xlsx',''+that.product+'_Futures');
// (1)'equity_future_export', (2)'xlsx',(3)''+that.product+'_Futures');
// there is only 3 parameters instead of 4, would it be correct?

_s2ab : function(s){

},
_eTTE : function(id, type, name, fn){
// id = equity_future_export
// type = xlsx

// name = where is "'+that.product+'_Futures" defined? There is no _Futures function here.
// fn = where is "fn" defined? there is only 3 parameter when calling eTTE function? so no fn?
var that=this;
var wb = XLSX.utils.table_to_book(document.getElementById(id), {sheet:"Sheet JS"});
// what is wb as returned result?
var wbout = XLSX.write(wb, {bookType:type, bookSST:true, type: 'binary'});
// what is wbout as returned result?
var fname = fn || name + '.' + type;
// what is fname as returned result? fn or ???.xlsx
try {
saveAs(new Blob([that._s2ab(wbout)],{type:"application/octet-stream"}), fname);
} catch(e) { if(typeof console != 'undefined') console.log(e, wbout); }
return wbout;
},


Does anyone have any suggestions?
Thanks in advance for any suggestions (^v^)