I am posting date object as unix timestamp.I use getTime() in javascript.

For example

when initializing in my .js file

as

```
firstDate = new Date("2019-08-04");

```

And then when I change value over date input

and firstDate.getTime() this returns timestamp without adding TimezoneOffset.

But without firstDate = new Date("2019-08-04"); assingnation,

when I change value over date input,It adds TimezoneOffset.

So For resolving this issue,I use 

```
var timestamp = firstDate.getTime() - 60000 * firstDate.getTimezoneOffset();

```

before posting timestamp to the server.

What is the reason of this ?