Shortest code to check if a number is in a range in JavaScript

Question

This is how I checkout to see if a number is in a range (in between two other numbers):

var a = 10,
    b = 30,
    x = 15,
    y = 35;

x < Math.max(a,b) && x > Math.min(a,b) // -> true
y < Math.max(a,b) && y > Math.min(a,b) // -> false

I have to do this math in my code a lot and I'm looking for shorter equivalent code.

This is a shorter version I came up with. But I am sure it can get much shorter:

a < x && x < b
true
a < y && y < b
false

But downside is I have to repeat x or y

Answer 1

Number.prototype.between = function (min, max) {
    return this > min && this < max;
};

if ((5).between(4, 6)) {
    alert('worked!');
}

var num = 6;
if (num.between(5, 7)) {
    alert('still worked!');
}

http://jsfiddle.net/jbabey/4jjRm/1/

Note that you need to surround number literals in parens, or the interpreter will think your property is a decimal point and blow up.