[Google Spreadsheets Script] Simple time tracking

script.js

function onOpen() {
    var ui = SpreadsheetApp.getUi();
    // Or DocumentApp or FormApp.
    ui.createMenu('Time tracking')
        .addItem('Setup', 'setupSpreadsheet')
        .addItem('Start task', 'startTask')
        .addItem('End task', 'endTask')
        .addToUi();
}

function durationFormula(rowNo) {
    return "=(D" + rowNo + " + E" + rowNo + ") - (B" + rowNo + " + C" + rowNo + ")"
}

function setupSpreadsheet() {
    var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
    var sheet = spreadsheet.getActiveSheet();

    // set date format
    var dateValidation = SpreadsheetApp
        .newDataValidation()
        .requireDate()
        .build();
    [
        sheet.getRange("B:B"),
        sheet.getRange("D:D")
    ].forEach(function (range) {
        range
            .setNumberFormat("yyyy-mm-dd")
            .setDataValidation(dateValidation);
    });
    // set time format
    [
        sheet.getRange("C:C"),
        sheet.getRange("E:E")
    ].forEach(function (range) {
        range
            .setNumberFormat("hh:mm");
    });
    sheet.getRange("F:F")
        .setNumberFormat("[h]:mm");

    // set title
    sheet.getRange("B2:G2")
        .setDataValidation(null)
        .setValues(new Array([
            'start', '',
            'stop', '',
            'duration', 'task'
        ]));
    // set width
    sheet
        .setColumnWidth(2, 150)
        .setColumnWidth(4, 150)
        .setColumnWidth(7, 200);
    // set initial formula
    sheet.getRange("F3")
        .setValue(durationFormula(3));
}

function appendTaskTime(rowNumber, offset) {
    var sheet = SpreadsheetApp
        .getActiveSpreadsheet()
        .getActiveSheet();

    var now = new Date();

    sheet.getRange(rowNumber, offset)
        .setValue(now.toLocaleDateString());
    sheet.getRange(rowNumber, offset + 1)
        .setValue(now.getHours() + ":" + now.getMinutes());
}

function endTask() {
    var sheet = SpreadsheetApp
        .getActiveSpreadsheet()
        .getActiveSheet();
    var rowNo = sheet.getLastRow();
    var value = sheet.getRange(rowNo, 4).getValue();
    if (value !== "") {
        return;
    }
    appendTaskTime(rowNo, 4);
    sheet.getRange(rowNo, 6)
        .setValue(durationFormula(rowNo));
}

function startTask() {
    var sheet = SpreadsheetApp
        .getActiveSpreadsheet()
        .getActiveSheet();
    var rowNo = sheet.getLastRow() + 1;
    endTask();
    appendTaskTime(rowNo, 2);
    sheet
        .setActiveRange(sheet.getRange(rowNo, 7));
}