javascript - Removing last comma

I read content from a file and then write it another file after editing . While editing , for each read line i put a comma at the end of line and then write it to the file. For the last read line i do not want to write a comma. How should i do it.?

 while(!inputFile.AtEndOfStream){
    var readLine =  inputFile.ReadLine();
    var omitChars = new RegExp("#define").test(readLine);
    if(omitChars==1){
        var stringReadPosition = readLine.substr(8);

        var finalString = stringReadPosition.replace(/\s+/g, ': ');
              asd = outputFile.Write(finalString.replace(/^(_)/, "") + ",\r\n");
    }
 }
 outputFile.Write("};\r\n");
 inputFile.Close();
 outputFile.Close();
}