@MooGoo's switch (true) will give you a Weird condition error in jsLint, so let's get a little more creative in case that's an issue, and, I think, increase readability a touch.

So we're not evaluating if each case is true or false; we're comparing if that case's value is equal to our switch term. So let's take advantage of that by throwing a shorthand if into our case statement and return our original switch term if the condition's true.

I'm also including a sort of real world example, where you want to have two "defaults" -- one if your term is outside of your "important" range in the positive direction, and another in case you're in the negative direction.

Key phrase: case (x > 0 ? x : null):

"If my term, x, is greater than zero, return x so that x === x and I take the case branch."

http://jsfiddle.net/rufwork/upGH6/1/

/*global document*/
/*jslint evil:true*/
var x = 10;

switch (x) {
    case (x > 0 ? x : null):
        document.write('ha ha ha!  I fooled switch AND jsLint!  Muhahahahaha!');
        break;
    case 0:
        document.write('zero is nothing.');
        break;
    case -1:
        document.write('low');
        break;
    case -2:
        document.write('lower');
        break;
    case -3: 
        document.write('lowest I care about');
        break;
    default: // anything lower than -3.
        document.write('TOO LOW!!!! (unless you cheated and didn\'t use an int)');
}
document.write('<br>done.');

Quick reply to @Sv443:

Do notice that the default: switch says, "unless you cheated and didn't use an int" and that short circuiting requires x === x when you return x.

But your point is a useful reminder that NaN is the only case where short circuiting can't apply.

That is, x must == x to short circuit in switch and, as MDN tells us, "NaN, and only NaN, will compare unequal to itself" (double or triple =).

That also means that switching on a NaN value (and only a NaN value) will always hit default in ANY switch because you can't match its value.

Here's the full quote from MDN:

NaN compares unequal (via ==, !=, ===, and !==) to any other value -- including to another NaN value. Use Number.isNaN() or isNaN() to most clearly determine whether a value is NaN. Or perform a self-comparison: NaN, and only NaN, will compare unequal to itself.

You could change the default logic to check what you have:

isNaN(x) ? document.write ('nan') : document.write('TOO LOW!!!! ...)');

Or you even could go full hipster like MDN suggests (but please don't ;^D):

x !== x ? document.write ('nan') : document.write('TOO LOW!!!! ...)');