How to alter this script to add another condition - if-statement

Question

I have this piece of code which has been working great for me, however, I need a minor alteration to it and don't know how to proceed.
I would like for 'Multiple Use' to be added as another condition, alongside 'Yes' for the onEdit() to work.
function numberToLetter(number){
// converts the column number to a letter
var temp = "";
var letter = "";
while (number > 0){
temp = (number - 1) % 26;
letter = String.fromCharCode(temp + 65) + letter;
number = (number - temp - 1) / 26;
}
return letter;
}
function obtainFirstBlankRow() {
var sheet = SpreadsheetApp.getActive().getSheetByName('Aug2019');
// search for first blank row
var col = sheet.getRange('A:A');
var vals = col.getValues();
var count = 0;
while (vals[count][0] != "") {
count++;
}
return count + 1;
}
function onEdit(e) {
var ss = SpreadsheetApp.getActiveSheet();
if (ss.getName() == 'ProspectiveSites' && e.range.getColumn() == 26) {
if (e.range.getValue() != 'Yes'){
Logger.log('test');
return;
}
var sourceSheet = SpreadsheetApp.getActive().getSheetByName('ProspectiveSites');
var targetSheet = SpreadsheetApp.getActive().getSheetByName('Aug2019');
//Logger.log('O' + e.getRow() + ':O' + e.getRow());
Logger.log(e);
Logger.log(e.range.getValue());
var cell15 = sourceSheet.getRange('O' + e.range.getRow() + ':O' + e.range.getRow()).getValue();
var cell24 = sourceSheet.getRange('X' + e.range.getRow() + ':X' + e.range.getRow()).getValue();
Logger.log(cell15);
Logger.log(cell24);
var row = obtainFirstBlankRow();
targetSheet.getRange(row, 1).setValue(cell15);
targetSheet.getRange(row, 2).setValue(cell24);
}
}

Answer 1

Solution
What stops you from adding another condition for the if statement? Please, take some time to research JS documentation, it will greatly help you in the long run (see useful links after the sample).
Modifications
This modification assumes that you need to exit if value is not equal to "Multiple use" and not equal to "Yes". Also, note that there are a few additional changes made for optimization purposes (I changed all comparison operators to strict as well).
Sample
/**
* onEdit simple trigger;
* #param {Object} event object;
*/
function onEdit(e) {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var actS = ss.getActiveSheet(); //active sheet === source sheet;
//access event object params;
var range = e.range;
var row = range.getRow();
var column = range.getColumn();
var value = range.getValue();
if (actS.getName()==='ProspectiveSites' && column===26) {
if (value!=='Yes'&&value!=='Multiple Use') {
Logger.log('test');
return;
}
var augS = ss.getSheetByName('Aug2019'); //target sheet;
var cell15val = actS.getRange('O'+row+':O'+row).getValue();
var cell24val = actS.getRange('X'+row+':X'+row).getValue();
var rowBlank = obtainFirstBlankRow();
var target = augS.getRange(rowBlank,1,1,2); //idx, first col, 1 row, 2 cols;
target.setValues([[ cell15val , cell24val ]]);
}
}
Useful links
if..else statement reference on MDN;
Comparison operators reference on MDN;
getRange() method reference;
setValues() method reference;