how can I get the current date minus 20 seconds in javascript?

Question

how can I get the current date minus 20 seconds in javascript? I can not figure out how to subtract 20 seconds to the current date in javascript how can I do, I get a negative value in this way

There is an easier way? thanks

var currentDate = new Date()
var day = currentDate.getDate()
var month = currentDate.getMonth() + 1
var year = currentDate.getFullYear()
var ora = currentDate.getHours()
var minuti = currentDate.getMinutes()
var secondi = currentDate.getSeconds()-20

Answer 1

Give this a shot:

new Date(Date.now() - 20000);

The Date.now() returns the milliseconds since Jan 1, 1970 00:00:00, so we just subtract 20000 milliseconds from that, and use the result to create a new date.

As @rjz noted, you'll need a shim for old IE. The MDN shim is below:

if (!Date.now) {
     Date.now = function() { return new Date().getTime(); }
}

Answer 2

I would do it something like this:

function DateOffset( offset ) {
    return new Date( +new Date + offset );
}

var twentySecondsAgo = DateOffset( -20000 );

// Should differ by 20 seconds (modulo 60)
alert(
    twentySecondsAgo.getSeconds() +
    '\n' +
    new Date().getSeconds()
);

With this code you don't need any shims or polyfills or any of that stuff. I just tested it in IE 5.5 and Netscape 4.79 and it works fine there! That's why I used alert() in the test instead of console.log(), so I could test it in those old browsers.