The comp.lang.javascript FAQ has a nifty little trick in the type conversion section for converting anything to an int and rather than possibly getting NaN, you will always receive a number.

It's all about the bitwise OR

The method uses the bitwise OR operator | with a non-impacting 0 operand to leverage the JavaScript native ToInt32 function otherwise unavailable within your code. Simply OR a variable and it will be a number.

var foo;
...much chaos ensues...

foo = foo|0; // convert foo to an int

Similar to the unary + operator, |0 will convert false and the empty string to 0 and true to 1. However, it will also convert invalids, such as undefined, "foo", or function foo() {} to 0.

Cryptic? Yes. Idiomatic? Yes. Nifty? I think so. I don't anticipate using it any time soon, as its applicability seems limited, but still something to have in the tool belt (and never use without annotation).

Check out the FAQ page for more info.