Trouble automating email from google sheets - google-apps-script

Question

I am very new to google script and cannot work out why my script is not functioning. When I try to run the code I get the following error code -
TypeError: Cannot read property "range" from undefined. (line 2, file "Code"
If anybody could give a novice some help that would be greatly appreciated!
function sendEmail(event){
var sheet = event.range.getSheet();
if(sheet.getName() !== 'Sheet1') {
// if it's not the correct sheet we end the function here
return;
}
var range = event.range;
var row = range.getRow(); // we get the index of the row of the
edited
cell
var dataRange = sheet.getRange("A" + row + ":C" + row);
var values = dataRange.getValues();
var rowValues = values[0];
var recipient = rowValues[0];
var email = rowValues[1];
var refillsNumber = rowValues[2];
if (refillsNumber = 2) {
// if 'refillsNumber' is not equal to 2 we end the function here
var message = 'Dear ' + recipient + ',\n\n'+ 'You have ' +
refillsNumber + ' remaining would you like to buy more?' + '\n\n' +
'Kind regards,' + '\n\n' + 'The revol team.';
var subject = 'Refill reminder';
MailApp.sendEmail(email,subject,message);
return
}
if (refillsNumber !== 0) {
return}
var message = 'Dear ' + recipient + ',\n\n'+ 'You have ' +
refillsNumber + ' remaining would you like to buy more? If not then
would you like to end your subsription?' + '\n\n' + 'Kind regards,'
+ '\n\n' + 'The revol team.';
var subject = 'Refill reminder';
MailApp.sendEmail(email,subject,message);
return
}
// in addition to this script which aims to send an email to the
customer when they only have 2 refill remaining -
/// I also want to set up a function that sends an email when they
have 0 refills remaining

Answer 1

Send Emails by Editing Column C
I changed the Sheet name and added an extra condition. I also commented out the MailApp.sends and replaced them with writes to the sidebar so that I could test it without trying to send emails.
You will need to create an onEdit trigger for this function.
function sendMailOnEdit(event){
var sheet = event.range.getSheet();
if(sheet.getName() !== 'Sheet2' || event.range.columnStart!=3) {return;}
var range=event.range;
var row=range.rowStart;
var dataRange = sheet.getRange(row,1,1,3);
var values=dataRange.getValues();
var rowValues=values[0];
var recipient = rowValues[0];
var email = rowValues[1];
var refillsNumber = rowValues[2];
if (refillsNumber==2) {
var message = 'Dear ' + recipient + ',\n\n'+ 'You have ' + refillsNumber + ' remaining would you like to buy more?' + '\n\n' + 'Kind regards,' + '\n\n' + 'The revol team.';
var subject = 'Refill reminder';
//MailApp.sendEmail(email,subject,message);
var html=Utilities.formatString('<br />Email: %s<br />Subject: %s<br />message: %s<br /><hr>', email,subject,message);
var userInterface=HtmlService.createHtmlOutput(html);
SpreadsheetApp.getUi().showSidebar(userInterface);
return
}
if (refillsNumber !== 0) {return}
var message = 'Dear ' + recipient + ',\n\n'+ 'You have ' + refillsNumber + ' remaining would you like to buy more? If not then would you like to end your subsription?' + '\n\n' + 'Kind regards,' + '\n\n' + 'The revol team.';
var subject = 'Refill reminder';
//MailApp.sendEmail(email,subject,message);
var html=Utilities.formatString('<br />Email: %s<br />Subject: %s<br />message: %s<br /><hr>', email,subject,message);
var userInterface=HtmlService.createHtmlOutput(html);
SpreadsheetApp.getUi().showSidebar(userInterface);
}
This is what my spreadsheet looks like:
And let me remind you that you cannot run this function without an event object.