Get diagonal animation steps for a grid (qunit tested)

gistfile1.js

module("Diagonale");

var getStep = function(index, cols) {

    if (index <= cols) {
        return index;
    }

    return index % cols === 0
        ? index / cols + (cols - 1)
        : Math.floor(index / cols) + index % cols;
};

/**
 * Tests results on a 3 column grid
 *
 *  1  2  3
 *  4  5  6
 *  7  8  9
 */
test("3 cols", function() {

    var cols = 3;

    equal(getStep(1, cols), 1, "Elemement 1 in step");
    equal(getStep(2, cols), 2, "Elemement 2 in step");
    equal(getStep(3, cols), 3, "Elemement 3 in step");

    equal(getStep(4, cols), 2, "Elemement 4 in step");
    equal(getStep(5, cols), 3, "Elemement 5 in step");
    equal(getStep(6, cols), 4, "Elemement 6 in step");

    equal(getStep(7, cols), 3, "Elemement 7 in step");
    equal(getStep(8, cols), 4, "Elemement 8 in step");
    equal(getStep(9, cols), 5, "Elemement 9 in step");
});


/**
 * Tests results on a 4 column grid
 *
 *  1  2  3  4
 *  5  6  7  8
 *  9 10 11 12
 */
test("4 cols", function() {
    
    cols = 4;

    equal(getStep(4, cols), 4, "Elemement 4 in step");
    equal(getStep(5, cols), 2, "Elemement 5 in step");
    equal(getStep(7, cols), 4, "Elemement 7 in step");
    equal(getStep(8, cols), 5, "Elemement 8 in step");
});

/**
 * Tests results on a 1 column grid
 *
 *  1
 *  2
 *  3
 */
test("1 col", function() {

    cols = 1;

    equal(getStep(1, cols), 1, "Elemement 1 in step");
    equal(getStep(2, cols), 2, "Elemement 2 in step");
    equal(getStep(3, cols), 3, "Elemement 3 in step");
});

/**
 * Creating an array with animation sequence
 */
test("Create a sequence", function() {

    var total    = 9,
        columns  = 3,
        sequence = [];

    for (var i = 1; i <= total; i++) {

        var stepNum = getStep(i, columns) - 1,
            step    = sequence[stepNum] = sequence[stepNum] ? sequence[stepNum] : [];

        step.push(i);
    }

    same(sequence[0], [1],     "Step 1");
    same(sequence[1], [2,4],   "Step 2");
    same(sequence[2], [3,5,7], "Step 3");
    same(sequence[3], [6,8],   "Step 4");
    same(sequence[4], [9],     "Step 5");

});