using date.js to combine date, time and convert to unix timestamp in javascript

I have two values

var date = "2012-08-10";
var time = "10:10";

Then I do

var dte = date + " " + time;

and

var dte = new Date(dte).getTime() / 1000;

The below link says it needs date.js to give right reults Converting Date and Time To Unix Timestamp

Can the above code give right results without date.js

Copyright Notice：Content Author:「san」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/49506020/using-date-js-to-combine-date-time-and-convert-to-unix-timestamp-in-javascript