Do not make copy of existing file in destination folder - google-apps-script

Question

I've been trying to copy contents from one folder to another folder in google drive using google app script. With some online help and documentation of google script, I was able to copy files from one folder to other but it copies all files from source folder to destination folder on time trigger, but I want only the new files to get copied in my destination folder and skip the present files that are already same in my source and destination folder.
I tried to check files by name before copying but couldn't find a way to compare files by name in two different folders of gdrive.
function CopyFiles() {
var SourceFolder = DriveApp.getFolderById('Sid');
var SourceFiles = DriveApp.getFolderById('Sid').getFiles();
var DestFolder = DriveApp.getFolderById('Did');
var DestFiles = DriveApp.getFolderById('Did').getFiles();
while (SourceFiles.hasNext())
{
var files = SourceFiles.next();
var dfiles = DestFiles.next();
if ( files == dfiles){
file.setTrashed(true);}
else{
var f = files.makeCopy(DestFolder);
}
}
}
What I want to achieve is that Script compares files by name in destination folder and if files by that name already exist than skip else, create a copy of that new file in the destination folder.

Answer 1

Copies files from source to destination if destination does have the same file names
In this version no files get trashed.
function CopyFiles() {
var srcFldr=DriveApp.getFolderById('srcId');
var srcFiles=srcFldr.getFiles();
var desFldr=DriveApp.getFolderById('desId');
var desFiles=desFldr.getFiles();
var dfnA=[];
while(desFiles.hasNext()) {
var df=desFiles.next();
dfnA.push(df.getName());
}
while(srcFiles.hasNext()) {
var sf=srcFiles.next();
if(dfnA.indexOf(sf.getName())==-1) {
sf.makeCopy(sf.getName(),desFldr);
}
}
}