title: overwrite an excel file with nodeJs
body: <p>i want to overwrite an excel file with sailsJs, but really i don't know how to do it.I tried node-xlsx,exceljs but none works for me.I don't want to create a new file but modify an existing file. is there anyone who have an idea of how to do it? Thanks in advance.
  this is my code:</p>
  
  <pre><code>var Excel = require("exceljs");
  excel:function(req,res){
  var workbook = new Excel.Workbook();
  workbook.xlsx.writeFile("test.xls")
  .then(function() {
  var sheet = workbook.addWorksheet("My Sheet");
  var worksheet = workbook.getWorksheet("My Sheet");
  worksheet.columns = [
          { header: "Id", key: "id", width: 10 },
          { header: "Name", key: "name", width: 32 },
          { header: "D.O.B.", key: "DOB", width: 10 }
      ];
  
  worksheet.addRow({id: 1, name: "John Doe", dob: new Date(1970,1,1)});
  worksheet.addRow({id: 2, name: "Jane Doe", dob: new Date(1965,1,7)});
  });
  
  } 
  </code></pre>
  
  <p>This created a file named "test.xls" but this file is empty and doesn't contain any of the informations i pass in like parameters of the row.</p>