calc time diff, node time_diff.js 2:30:00 5:30:00, will output: 03:00:00

time_diff.js

#!/usr/bin/env node
if (!process.argv[2] || !process.argv[3]) {
    console.log('usage node time_diff hh:mm:ss hh:mm:ss');
    process.exit(1);
}
const timeToSec     = (time) => time.split(':').reduce((acc, v) => acc * 60 + parseInt(v), 0);
const diffInSeconds = (time1, time2) => timeToSec(time2) - timeToSec(time1); 
const hhmmss = (secs) => {
    var minutes = Math.floor(secs / 60);
    secs = secs % 60;
    var hours = Math.floor(minutes / 60);
    minutes = minutes % 60;
    return pad(hours) + ":" + pad(minutes) + ":" + pad(secs);
    function pad(num) {
        return ("0" + num).slice(-2);
    }
};
try {
    console.log(hhmmss(diffInSeconds(process.argv[2], process.argv[3])));
}
catch (err) {
    console.log('usage node time_diff hh:mm:ss hh:mm:ss');
    process.exit(1);
}