How to get the current date or/and time in seconds

I use this:

Math.round(Date.now() / 1000)

No need for new object creation (see doc Date.now())

Date.now()-Math.floor(Date.now()/1000/60/60/24)*24*60*60*1000

This should give you the milliseconds from the beginning of the day.

(Date.now()-Math.floor(Date.now()/1000/60/60/24)*24*60*60*1000)/1000

This should give you seconds.

(Date.now()-(Date.now()/1000/60/60/24|0)*24*60*60*1000)/1000

Same as previous except uses a bitwise operator to floor the amount of days.

On some day in 2020, inside Chrome 80.0.3987.132, this gives 1584533105

~~(new Date()/1000) // 1584533105
Number.isInteger(~~(new Date()/1000)) // true

There is no need to initialize a variable to contain the Date object due to the fact the Date.now() is a static method which means that is accessible directly from an API object's constructor.

So you can just do this

document.write(Date.now()) // milliseconds

document.write(Date.now()/1000) // seconds

Something fun

Live update of seconds since January 1, 1970 00:00:00 UTC

let element = document.getElementById('root')

const interval = setInterval(() => {
  let seconds = Math.round(Date.now()/1000)
  element.innerHTML = seconds
},1000)

Seconds since January 1, 1970 00:00:00 UTC 
<h1 id='root'></h1>

To get today's total seconds of the day:

getTodaysTotalSeconds(){
    let date = new Date();        
    return +(date.getHours() * 60 * 60) + (date.getMinutes() * 60) + date.getSeconds();
}

I have add + in return which return in int. This may help to other developers. :)

if you simply need seconds in THREE JS, use one of the code bellow in function uses window.requestAnimationFrame()

let sec = parseInt(Date.now().toString()[10]); console.log(' counting Seconds => '+ sec );

or let currentTime= Date.now();

let secAsString= time.toString()[10];

let sec = parseInt(t);

console.log('counting Seconds =>'+ sec );