<apex:page controller="uploadDataTosObject" apiVersion="36.0">
[Code....]
    <apex:form>
        <script>
            function setVal(result)
            {
                document.getElementById("{!$Component.hdnField}").value =result;
            }
        </script>
        <apex:inputHidden id="hdnField" value="{!myblob}" />
        <apex:commandButton value="Post Page" action="{!post}" />
    </apex:form>
    <script>
        setVal();
    </script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/es5-shim/4.5.7/es5-shim.js">
   </script>
   <script src="https://cdnjs.cloudflare.com/ajax/libs/xlsx/0.8.0/jszip.js">    </script>
   <script src="https://cdnjs.cloudflare.com/ajax/libs/xlsx/0.8.0/xlsx.js"></script>
     [Code...]
            function to_csv(workbook) {
                var result = [];
                workbook.SheetNames.forEach(function(sheetName) {
                    var csv = X.utils.sheet_to_csv(workbook.Sheets[sheetName]);
                    if(csv.length > 0){
                        result.push("SHEET: " + sheetName);
                        result.push("");
                        result.push(csv);
                    }
                });
                output = setval(result.join("n"));
                return result.join("n");
            }
[Code...]
    </body>
</apex:page>

public with sharing class uploadDataTosObject {
    public String myblob {get; set;}
    public void post(){
        system.debug(myblob);
    }
}