Is there a slicker way of doing this?

Question

I seem to handle special cases like this somewhat frequently. There's got to be a more concise syntax or construct:

var x = solveForX(); /* some slow calculation here */
if (x < 0)
{
    x = 0;
}

This is equivalent, but doesn't feel any more elegant:

var x;
x = (x = solveForX()) < 0 ? 0 : x;

Maybe there's a bit shift trick?

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Update: I ran some benchmarks in Firefox to compare my two favorite answers - the one I accepted, and Peter Ajtai's. Turns out Peter's is quite a bit faster! Running 1,000,000 iterations of each (I also ran a version that caches Math.max to see how much time the lookup contributed) shows that Peter's runs in under half the time of the Math.max version, even with max caching.

That said, a million iterations even with the "slowest" method still takes only 0.25 seconds.

Answer 1

How about

var x = Math.max(solveForX(), 0);

Answer 2

Something like:

x = Math.max(0, solveForX());

Answer 3

Why do you have a problem with the first example? Although there's a few more lines, it's a lot easier to read and follow.

Answer 4

(x < 0) && (x = 0);

Edit: Removed the if statement. Thanks Andreas.

This is one line, and it's clear what it does (in my personal opinion) - if you're familiar with boolean short circuit evaluation.

The above makes use of boolean short circuit evaluation. This can be very useful in certain situations (especially pointer arithmetic in C++, but boolean short circuit evaluation also works in Javascript).

x = 0 only evaluates if x < 0.

Here are two examples:

This alerts 1:

<script type="text/javascript">
    var x = 1;
    (x < 0) && (x = 0);
    alert(x);
</script>

This alerts 0:

<script type="text/javascript">
    var x = -1;
    (x < 0) && (x = 0);
    alert(x);
</script>

Answer 5

I'd decorate the original solveForX function.

function returnNonNegative(fn) {
    function _f() {
        var x = fn();
        if (x < 0) {
            x = 0;
        }
        return x;
    }
    return _f;
}

solveForX = returnNonNegative(solveForX);

In this particular case, using Math.max seems to be fine, but this pattern provides a generic solution for this type of problems.

Answer 6

If you want to get real geeky with this, make a prototype for the number object. You will maintain the value, but the special formatted output for negatives could be managed easily with some output method.

http://www.w3schools.com/jsref/jsref_prototype_num.asp

Answer 7

The accepted answer is perfect. If you want to accomplish the same without a function call, I believe that this is most concise:

var x;
(x = solveForX()) > 0 || (x = 0);

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(In Safari, this implementation is a whole 7% faster than Math.max(), which is probably not worth caring about)