moment.js concatenate date and time

The fail is trying on concatenate the values, test with something like this:

let initialdate = '2016-10-01';
let start_time = '19:04:10';
let enddate = '2016-10-01';
let end_time = '19:04:20';

let datetimeA = moment(initialdate + " " + start_time);
let datetimeB = moment(enddate + " " + end_time);

console.log(datetimeA.format());
console.log(datetimeB.format());

let datetimeC = datetimeB.diff(datetimeA, 'seconds');

console.log(datetimeC);

Concatenate the date and time strings and parse them as one, e.g.

var date = '23/02/2017';
var time = '15:42';

var dateTime = moment(date + ' ' + time, 'DD/MM/YYYY HH:mm');

console.log(dateTime.format('YYYY-MM-DD HH:mm'))

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