title: how to append to a excel file in nodejs
body: <p>i am currently working on a form which will take user input and add it to one row of an excel sheet, as of now i have managed to make excel sheet using 3rd party plugins(node-xls to be specific).
  issue arises if i wanna add another row to the excel , it deletes the old entry and adds the new instead of appending the data to the next row.</p>
  
  <p>tried reading the excel and then concatenating the buffers and writing the file again, but turns out it is corrupting the file and is rendering it unusable.</p>
  
  <p>How do i append data to the end of the excel sheet? i am new to nodejs and buffers</p>
  
  <pre><code>var fs = require('fs');
  var NodeXls = require('node-xls');
  var tool = new NodeXls();
  var xls = tool.json2xls({firstName: "arjun", lastName: "u", dob:"12/3/2008"}, {order:["firstName", "lastName", "dob"]});
  fs.appendFile('output.xlsx', xls, 'binary', function(err){
  if(err)
    alert("File is readOnly or is being used by another application,  please close it and continue!");
  });
  </code></pre>