Get Spreadsheets from a folder and modify them - google-apps-script

Question

I have a folder called "Adform" in my Drive and I want to take all the spreadsheets from there and modify them by adding new columns, change headers.
At this point I managed to get the files name, one by one, but I don't know how to use SpreadSheetApp to modify those Spreadsheets.
var folders = DriveApp.getFoldersByName('Adform');
while (folders.hasNext()) {
var files = folders.next().getFiles();
while (files.hasNext()) {
var file = files.next();
Logger.log(file.getName());
}
}

Answer 1

How to loop through all the Spreadsheets in a Drive folder
You are almost there. The best way in my opinion is to check if the mime type of the file is application/vnd.google-apps.spreadsheet, and if so, get the id. Then pass this id to another function that will modify the Spreadsheet in any way that you want.
function myFunction() {
var folders = DriveApp.getFoldersByName('Adform');
while (folders.hasNext()) {
var files = folders.next().getFiles();
while (files.hasNext()) {
var file = files.next();
// Check if file is a spreadsheet
if (file.getMimeType() === "application/vnd.google-apps.spreadsheet") {
// Call the function to modify the spreadsheet with the file id
modifySpreadhsheet(file.getId())
}
}
}
}
function modifySpreadsheet(id) {
// Open the file with the id
var file = SpreadsheetApp.openById(id);
// Get all the sheets
var sheets = file.getSheets()
// Get the first sheet
var firstSheet = sheets[0]
// Get the range that contains all the data in that sheet
var range = firstSheet.getDataRange();
// Get all the values in that range
var values = range.getValues();
Logger.log(values)
}
This sample function will just get the first sheet of the spreadsheet and then Log all the data within that spreadsheet to the logger.
Then you can use functions like setValues(values) to modify the content as needed.
References
getMimeType()
getId()
openById(id)
getSheets()
getDataRange()
getValues()