google sheets multiple drop down code example

Example: google sheet text field to add from multiple dropdown

function onEdit(e) {
var oldValue;
var newValue;
var ss=SpreadsheetApp.getActiveSpreadsheet();
var activeCell = ss.getActiveCell();
if(activeCell.getColumn() == 3 && activeCell.getRow() == 1 && ss.getActiveSheet().getName()=="Sheet1") {
newValue=e.value;
oldValue=e.oldValue;
if(!e.value) {
activeCell.setValue("");
}
else {
if (!e.oldValue) {
activeCell.setValue(newValue);
}
else {
activeCell.setValue(oldValue+', '+newValue);
}
}
}
}