moment().duration().milliseconds();

npm install moment

const moment = require('moment'); 
  
let durationOne = 
    moment.duration(900, 'milliseconds'); 
let durationTwo =  
    moment.duration(5750, 'milliseconds'); 
  
// This returns 900 as the number of 
// milliseconds is less than a whole second 
console.log( 
    "durationOne milliseconds is:", 
    durationOne.milliseconds() 
) 
  
// This returns 750 as the number of milliseconds 
// is greater than 5 seconds, and therefore 
// returns the value of milliseconds 
// of the next second (next 750 milliseconds) 
console.log( 
    "durationTwo milliseconds is:", 
    durationTwo.milliseconds() 
)

durationOne milliseconds is: 900
durationTwo milliseconds is: 750

const moment = require('moment'); 
  
let durationA = 
    moment.duration(1, 'seconds'); 
let durationB =  
    moment.duration({ seconds: 5, milliseconds: 250 }); 
  
// The asMilliseconds() method will return the 
// length of the duration in milliseconds 
console.log( 
    "Length of durationA in milliseconds is:", 
    durationA.asMilliseconds() 
) 
console.log( 
    "durationA milliseconds is:", 
    durationA.milliseconds() 
) 
  
console.log( 
    "Length of durationB in milliseconds is:", 
    durationB.asMilliseconds() 
) 
  
console.log( 
    "durationB milliseconds is:", 
    durationB.milliseconds() 
)

Length of durationA in milliseconds is: 1000
durationA milliseconds is: 0
Length of durationB in milliseconds is: 5250
durationB milliseconds is: 250