how to add into CSV file

Hi everyone .. Actully i have an array and i need to add this values to a file called demo.csv.. the array is added successful in the file but if i run the app once again with new array of data the file is recreated and old data is lost and the new array objects are visible.... can help me pls

var array = []; array.push('cd'); array.push('cc'); array.push('sa');

var file = Titanium.Filesystem.getFile(Titanium.Filesystem.applicationDataDirectory , 'Demo.csv'); if(!file.exists()){ file.createFile(); } var dataString = array.join(',');

file.write(dataString);