Javascript: convert negative number into binary

dec2bin.js

// Handler negtive number into binary.
// The code following is really meanless for number itself is depend on it's
// length. For instance, in bit operation, number will be treated as 32 bit.
// @see http://stackoverflow.com/questions/4338315/javascript-inverting-a-binary-value-of-a-number
function dec2Bin(dec)
{
    if(dec > 0) {
        return dec.toString(2);
    }
    else {
        //make the number positive
        dec = Math.abs(dec);
        //get the first compliment
        var res = dec ^ parseInt((new Array(dec.toString(2).length+1)).join("1"),2);
        //get the second complimet
        return (res+1).toString(2);
    }
}