01. Day of Week

function dayOfWeek(input) {
    let num = parseInt(input[0]);

    if (num == 1)
        console.log('Monday');
    else if (num == 2)
        console.log('Tuesday');
    else if (num == 3)
        console.log('Wednesday');
    else if (num == 4)
        console.log('Thursday');
    else if (num == 5)
        console.log('Friday');
    else if (num == 6)
        console.log('Saturday');
    else if (num == 7)
        console.log('Sunday');
    else
        console.log('Error');
}

Второ решение (switch):

function dayOfWeek(input) {
    let num = parseInt(input[0]);

    switch (num) {
        case 1:
            console.log('Monday');
            break;
        case 2:
            console.log('Tuesday');
            break;
        case 3:
            console.log('Wednesday');
            break;
        case 4:
            console.log('Thursday');
            break;
        case 5:
            console.log('Friday');
            break;
        case 6:
            console.log('Saturday');
            break;
        case 7:
            console.log('Sunday');
            break;
        default:
            console.log('Error');
            break;
    }
}

Решение с тернарен оператор:

function dayOfWeek(input) {
    let num = parseInt(input[0]);

    console.log(
        num == 1 ? "Monday" :
        num == 2 ? "Tuesday" :
        num == 3 ? "Wednesday" :
        num == 4 ? "Thursday" :
        num == 5 ? "Friday" :
        num == 6 ? "Saturday" :
        num == 7 ? "Sunday" : "Error"
    );
}

Решение с колекция и тернарен оператор:

function dayOfWeek(input) {
    let num = parseInt(input[0]);

    let dayOfWeek = ["Error", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"];

    console.log(dayOfWeek[(num > 0 && num < dayOfWeek.length ? num : 0)]);
}