Javascript function that calculates the difference between two datetime in hours

calculateDatetimeDeltaHours.js

/**
 * Calculates the difference between two datetime in hours
 * @param  {String}  Current datetime (any format compatible with Date)
 * @param  {String}  Start datetime (any format compatible with Date)
 * @return {Integer} The difference between Current datetime and Start datetime in hours
 */
function calculateDatetimeDeltaHours(datetimeCurrent, datetimeStart) {
    var datetimeCurrent = new Date(datetimeCurrent);
    var datetimeStart   = new Date(datetimeStart);
    var deltaHours = Math.abs(datetimeCurrent - datetimeStart) / 36e5
    return deltaHours;
}

// In the following example I put into deltaHours variable the return of calculateDatetimeDeltaHours function
var deltaHours = calculateDatetimeDeltaHours("04/13/2015 12:04:02", "04/13/2015 11:04:02");
// Then I print the difference, in hours, between the two timestamps
console.log(deltaHours);

You can try the code here:
https://jsfiddle.net/0opfanfL/