sort method in array

In javascript, if we declare an array and sort it, it doesn't sort it as numbers, it always perform sort like strings.
for e.g

Code:

var array1={1,33,4,56,7,99,9};
array1.sort();
document.write(array1);

this wont return the correct result. how to perform a number sort.

 

Code:

var array1=[1,33,4,56,7,99,9];
array1.sort(sortNumber);
document.write(array1);
function sortNumber(a,b)
{
	return a - b;
}

 

Reverse sort

Code:

var array1=[1,33,4,56,7,99,9];
array1.sort(sortNumber);
document.write(array1);
function sortNumber(a,b)
{
	return b - a;
}