Условия

// Условие If

if (condition1)
   alert("Hello!")

else if (condition2 && condition3) {
   alert("Bye-bye!")
}

else {
   alert("Unknown situation")
}

hours += (theHour >= 12)? "PM": "AM";

// Условие Switch

switch (new Date().getDay()) {
    case 1:
        day = "Monday";
        break;
    case 2:
        day = "Tuesday";
        break;
    case 3:
        day = "Wednesday";
        break;
    case 4:
        day = "Thursday";
        break;
    case 5:
        day = "Friday";
        break;
    case 6:
        day = "Saturday";
        break;
    default;
        day = "Sunday";
}