How to Calculate Date Differences in JavaScript?

Determining Date Differences in JavaScript

Finding the difference between two dates in JavaScript involves utilizing the Date object and its milliseconds value. For instance, let's consider the following example:

<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>

This calculation provides the number of milliseconds between the current date (a) and the specified date (b), representing the elapsed time. To obtain the difference in seconds, simply divide the milliseconds by 1000 and round it to an integer:

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

If you require the difference in larger time units, such as minutes, hours, or even days, you can employ the get_whole_values function demonstrated below:

<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>

This function takes a base value (e.g., milliseconds) and an array of time fractions (e.g., seconds per minute, minutes per hour) as parameters. It then calculates the whole amount of each time unit and the remainder in the original unit.

For instance, consider the following example:

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

This result indicates that 72000 milliseconds translates to 0 milliseconds, 12 seconds, and 1 minute.

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