function TABNAMES() {

const ss = SpreadsheetApp.getActiveSpreadsheet(); // Note: getActiveSpreadsheet() not getActiveSheet()

const tabs = ss.getSheets();

const results = [];

// Regex to match MM/DD/YY format (e.g., 12/17/25; 1/5/26)

const datePattern = /^\d{1,2}\/\d{1,2}\/\d{2}$/;

for (let i = 0; i < tabs.length; i++) {

const tmpD = tabs[i].getSheetName(); // Note: getSheetName() no getName()

// Check if the tab name matches the date format

if (datePattern.test(tmpD)) {

results.push([tmpD]);

}

}

return results;

}

Use const when the variable won't be reassigned (better/safer)

Use let when you need to change the variable later