rotate 2 dimensional bitmap in JavaScript

gistfile1.txt

var rotate90 = function (orig) {
    var rotated = [];
    for (var colIdx = 0; colIdx < orig[0].length; colIdx++) {
        var reverseCol = [],
            col;
        for (var rowIdx = 0; rowIdx < orig.length; rowIdx++) {
            reverseCol.push(orig[rowIdx][colIdx]);
        }
        col = reverseCol.reverse();
        rotated.push(col);
    }
    return rotated;
};

var bitmap = [[8,7,4,3],[6,5,8,9],[7,6,5,2],[9,8,6,7]];
// rotate90(bitmap) yields: [[9,7,6,8],[8,6,5,7],[6,5,8,4],[7,2,9,3]]