function isEven(num)
{
	// if(num % 2 == 0){return true;}else{return false;} //<–old
	return !(num%2);//shorter
	// return !(num & 1);//seems the fastest one
}
//
trace(isEven(2));//–> true
trace(isEven(3));//–> false

/////////////////

function isEven2(num : Number)
{
	return num % 2 == 0;
}

function isEven3(num : Number)
{
	return num & 1 == 0;
}

trace( isEven2( 5 ) );
trace( isEven2( 5 ) );

http://www.bit-101.com/blog/?p=729

AS3: Odd or Even

ActionScript 3