Google App Script to trigger on cell value change - google-apps-script

Question

I am a newbie and have been using a simple App Script to send out emails with triggers onEdit and onChange. However, my Worksheet has over ten sheets and any edits/changes (done by me or by computations) in any of the sheets sends out an email, causing unintended spam! To avoid this, if I could use some code that sends the email based only on ANY CHANGE to a specific cell's value, in a specific sheet, my problem would be solved. My outgoing email message is short and the whole message is in just ONE cell (C2). If I can add a line of code which monitors for ANY change in that cell C2, and sends out an email if there is a change, that's it! I'd be done. My Script is as follows:
function sendEmail(){
var ss = SpreadsheetApp.getActiveSpreadsheet()
var sheet1=ss.getSheetByName('Email');
var emailAddress = sheet1.getRange(2,1).getValue();
var subject = sheet1.getRange(2,2).getValue();
var message = sheet1.getRange(2,3).getValue();
MailApp.sendEmail(emailAddress, subject, message);
}

Answer 1

Answer:
You can do this with an onEdit() and a conditional.
Code Example:
function onEdit(e) {
const specificSheet = "Email" // for example
const specificCell = "C2" // for example
let sheetCheck = (e.range.getSheet().getName() == specificSheet)
let cellCheck = (e.range.getA1Notation() == specificCell)
if (!(sheetCheck && cellCheck)) {
return
}
else {
sendEmail()
}
}
Rundown of this function:
Defines the sheet and A1 notation of the specific cell to check
Gets the Sheet and the A1 notation of the cell which was just edited
Returns if either the Sheet or the Cell are not the defined specific cell (using De Morgan's law)
Runs sendEmail() if the cell and Sheet are correct
References:
Event Objects | Apps Script | Google Developers
Simple Triggers | Apps Script | Google Developers
De Morgan's laws - Wikipedia

Answer 2

Working from the answer, this is how it ended up for me since I had several ranges to check:
function onEdit(e){
if(wasEdited(e, range1)){ // e.g. range1 = "Sheet1!A5"
// handle range1 change
}
if(wasEdited(e, range2)){ // e.g. range2 = "Sheet1!A7"
// handle range2 change
}
}
function wasEdited(e, range){
let tab = getTabFromA1Range(range)
let cell = getRangeFromA1Range(range)
return e.range.getSheet().getName() == tab && e.range.getA1Notation() == cell
}
function getTabFromA1Range(a1Range){
return a1Range.substring(0, a1Range.indexOf("!"))
}
function getRangeFromA1Range(a1Range){
return a1Range.substring(a1Range.indexOf("!")+1)
}

Answer 3

On further research, the following solution seems to work the best:
function sendEmail(){
Utilities.sleep(30000);
var ss=SpreadsheetApp.getActiveSpreadsheet();
var data=ss.getActiveSheet().getActiveCell().getA1Notation();
var sheetname = ss.getActiveSheet().getName();
var sheet1=ss.getSheetByName('Email');
var emailAddress = sheet1.getRange(2,1).getValue();
var subject = sheet1.getRange(2,2).getValue();
var message = sheet1.getRange(2,3).getValue();
if(data.indexOf('A:C')!=-1.23456789) {
MailApp.sendEmail(emailAddress, subject, message);
}
};
The key seems to be the "if statement" on line 10. Please note the time delay of half a minute I added to the script. This is because without it, on the trigger activating, the previous email was going out instead of the current one. Obviously my app has a slight delay in syncing and the trigger fired before all the current data got populated in the relevant cell!