Update 2nd column based on access from first column - google-apps-script

Question

I need to put the current date & time (on an individual row basis) in column K of my google docs spreadsheet, if either of column I or J is changed. This is my first attempt at using google scripts.
I've located a function that will do the time (and I'm hoping I can figure out how to do the date), but I don't know how to check for changes in cells, and update other cells. So for example if row 10 column I or J changes, row 10 column K should get the current date & time.
function myFunction() {
var d = new Date();
var timeStamp = d.getTime(); // Number of ms since Jan 1, 1970
// OR:
var currentTime = d.toLocaleTimeString(); // "12:35 PM", for instance
}

Answer 1

You can give this a shot - it uses string formatting to put the current date in the proper format (you can adjust as you need). One important thing to note: regardless of what you do here, the value will be displayed according to whatever formatting you have specified in the spreadsheet itself. Therefore if you don't do anything, the result is going to look like the traditional datetime representation. If you want it to appear in the format you specify, you can do two things: 1.) convert the entire column to text using the spreadsheet's Format menu; or 2.) (my choice) prefix the value you write with a ', which will essentially turn it into a string (that is what is done in the code below). Hope this helps.
function onEdit() {
var s = SpreadsheetApp.getActiveSheet();
// This was "MySheet" for me - change to whichever sheet you want to test
if( s.getName() == "MySheet" ) {
var r = s.getActiveCell();
// Check if the column is either I or J
var currColumn = r.getColumn();
if( currColumn == 9 || currColumn == 10) {
// If so, set dateCell = the current row at column J
var dateCell = s.getRange(r.getRow(), 11);
// Format the current date into datetime format (adjust to display how you want)
var dateTime = Utilities.formatDate(new Date(), "GMT-8", "MMM-dd-yyyy h:mm a");
// Set the cell
dateCell.setValue("'" + dateTime);
}
}
};