Hide Old Rows for Google Docs using Apps Script

gistfile1.js

/**
 * Looks for rows with old dates, and hides them if so. 
 * It finds the date column my checking the first column for the word 'Date'.
 */
function hideOldRows(colNum) {
  var sheet = SpreadsheetApp.getActiveSheet();
  var header = sheet.getRange(1, 1, 1, sheet.getLastColumn());
  var colNum = header.getValues()[0].indexOf('Date') + 1;
  if (colNum === 0) {
    Logger.log(header.getValues());
    throw Error('Could not find the word Date on the first row');
  }
  var rows = sheet.getRange(1, colNum, sheet.getLastRow(), 1);
  var numRows = rows.getNumRows();
  var values = rows.getValues();
  

  for (var i = 0; i <= numRows - 1; i++) {
    var row = values[i];
    if (isDate(row[0]) && isOld(row[0])) {
      sheet.hideRows(i + 1);
    }
  }
};

function isDate(dateString) {
  return (new Date(dateString)) != "Invalid Date"; // notice not !==
}
  

function isOld(dateString) {
  assert(isDate(dateString));
  var inDate = (new Date(dateString)).getTime();
  var yesterday = new Date();
  yesterday.setDate(yesterday.getDate() - 1);
  
  return yesterday > inDate;
}

function assert(b, msg) {
  msg = msg || "default message";
  if (!b) {
    throw Error(msg)
  }
}
function test() {
  assert(isOld('Fri Jan 04 00:00:00 GMT-05:00 2013'));
  assert(!isOld('Fri Jan 04 00:00:00 GMT-05:00 2018'));
}
  

/**
 * Adds a custom menu to the active spreadsheet, containing a single menu item
 * for invoking the readRows() function specified above.
 * The onOpen() function, when defined, is automatically invoked whenever the
 * spreadsheet is opened.
 * For more information on using the Spreadsheet API, see
 * https://developers.google.com/apps-script/service_spreadsheet
 */
function onOpen() {
  var sheet = SpreadsheetApp.getActiveSpreadsheet();
  var entries = [{
    name : "Hide Old Rows",
    functionName : "hideOldRows"
  }];
  sheet.addMenu("Scripts", entries);
};

Hello. I have tried this script in one of my spreadsheets and it works great. But if i want the script to work for all sheets in a spreadsheet, how would I do that? I am new to github, so please excuse me if this isn't the right place for newbee questions. I will then try elsewhere.

What I have tried, is to merge your script whith the second script ("edit:working") in this tread:
http://stackoverflow.com/questions/16992771/how-can-i-run-a-google-script-automatically-on-multiple-sheets-in-the-same-sprea

But I haven't succeded yet. Thank you in advance for any help.

Hi theicfire!

How would you do the above but minus 7 days? So in other words, I'd like to show rows with "TODAY-7 Days".

Thank you!