How can I make the command work on page specific - css

Question

Thank you in advance for your help. How can I make the following command work only on the page named "customer" and not on other pages?
function onEdit(e) {
if (e.range.columnStart > 9)
return;
e.source.getActiveSheet().getRange(e.range.rowStart, 12).setValue(new Date());
}

Answer 1

If you want that code to run only inside a given page, you should include that code only in that page.
But in case you have a general js that you are going to include anywhere and you want to add logic to it so that it can make guesses on which page is loaded when it's running, you can read the value of window.location.href that will return the entire url of the page currently loaded in viewport:
var isCurrentPageCustomer = false;
//this regex will extract the final part of the url after the last slash (/)
//so if the url was http://mydomain/path/to/page the match will look for /page
var match = /\/([^/]+)$/.exec(window.location.href);
if (match != null) {
//result is holding "page" without the trailing slash (/)
result = match[1];
//if that part (eg.: 'page') matches 'customer', switch the flag=true
if (result === 'customer') isCurrentPageCustomer = true;
}
if(isCurrentPageCustomer)
console.log('current page is customer.');
else
console.log('current page is NOT customer.');
But it turned out later that you meant to run some code only when the current active sheet (in Google Sheets) is named customer. In that case I just changed your onEdit handler function and used the property name of the active sheet to decide to return from the function instantly if it doesn't match with 'customer'
function onEdit(e){
//if the name of the active sheet is not 'customer'
if (e.source.getActiveSheet().getName() != 'customer')
//exits the function without executing the rest of its code
return;
//the rest of your code here
}