JavaScript で日付の違いを計算するにはどうすればよいですか?

<code class="javascript">var a = new Date(); // Current date now.
var b = new Date(2010, 0, 1, 0, 0, 0, 0); // Start of 2010.
var d = (b - a); // Difference in milliseconds.</code>

<code class="javascript">var seconds = parseInt((b - a) / 1000);</code>

<code class="javascript">function get_whole_values(base_value, time_fractions) {
    time_data = [base_value];
    for (i = 0; i < time_fractions.length; i++) {
        time_data.push(parseInt(time_data[i] / time_fractions[i]));
        time_data[i] = time_data[i] % time_fractions[i];
    };
    return time_data;
};</code>

<code class="javascript">console.log(get_whole_values(72000, [1000, 60])); // [0, 12, 1]</code>