calculate the median of an array with javascript

median.js

function median(values) {

    values.sort( function(a,b) {return a - b;} );

    var half = Math.floor(values.length/2);

    if(values.length % 2)
        return values[half];
    else
        return (values[half-1] + values[half]) / 2.0;
}

var list1 = [3, 8, 9, 1, 5, 7, 9, 21];
median(list1);

I would also check the length first. if it is zero return. no need to proceed further.