在JavaScript中用switch语句编写if..else语句

Question

How can I write this if..else statement with a switch statement in JavaScript?

var hour = new Date().getHours();
var msg = "";
if (hour >= 0 && hour < 6) {
    msg = "بامداد شما بخیر !";
} else if (hour >= 6 && hour < 11) {
    msg = "صبح شما بخیر !";
} else if (hour >= 11 && hour < 15) {
    msg = "ظهر شما بخیر !";
} else if (hour >= 15 && hour < 20) {
    msg = "عصر شما بخیر !";
} else if (hour >= 20 && hour < 24) {
    msg = "شب شما بخیر !";
} else {
    msg = "ساعت وارد شده نامعتبر است !";
}
print(hour);
print("------------------------");
print(msg);

Answer 1

Since hour has just 24 discrete values, you could just handle all of them in a switch-case:

switch (hour) {
case 0:
case 1:
case 2:
case 3:
case 4:
case 5:
    msg = "بامداد شما بخیر !";
    break;
case 6:
case 7:
case 8:
case 9:
case 10:
    msg = "صبح شما بخیر !";
    break;
case 11:
case 12:
case 13:
case 14:
    msg = "ظهر شما بخیر !";
    break;
case 15:
case 16:
case 17:
case 18:
case 19:
    msg = "عصر شما بخیر !";
    break;
default:
    msg = "شب شما بخیر !";
}

But honestly, isn't a wasted effort. Using if-else is much more appropriate.

Answer 2

I'll just say at the outset that I wouldn't rewrite it as a switch . But I would definitely change it. (I'll do the switch below, though.)

First, your "ساعت وارد شده نامعتبر است !" case will never happen. getHours returns a number between 0 and 23, inclusive. So there's no need to handle the case of < 0 or >= 24 .

Here's how I'd write it:

var hour = new Date().getHours();
var msg;
if (hour < 6) {
    msg = "بامداد شما بخیر !";
} else if (hour < 11) {
    msg = "صبح شما بخیر !";
} else if (hour < 15) {
    msg = "ظهر شما بخیر !";
} else if (hour < 20) {
    msg = "عصر شما بخیر !";
} else {
    msg = "شب شما بخیر !";
}
print(hour);
print("------------------------");
print(msg);

Note how we're not having to write our limits in two places. There's no need for it, since we won't evaluate later else if s if the earlier if was true.

Now, for the actual switch , we do something similar, using the fact that JavaScript's switch is more powerful than in many similar-looking languages (JavaScript's switch is basically just an if/else if ):

var hour = new Date().getHours();
var msg;
switch (true) {
    case hour < 6:
        msg = "بامداد شما بخیر !";
        break;
    case hour < 11:
        msg = "صبح شما بخیر !";
        break;
    case hour < 15:
        msg = "ظهر شما بخیر !";
        break;
    case hour < 20:
        msg = "عصر شما بخیر !";
        break;
    default:
        msg = "شب شما بخیر !";
        break;
}
print(hour);
print("------------------------");
print(msg);

How that works: JavaScript's switch allows the case labels to be expressions . It evaluates each case in source code order against the value you give in the switch , taking the first case that matches. If no cases match, it uses the default (regardless of where the default is in the source code).

Again: I wouldn't do that. But the question was how to do it. :-)