moment().duration().toJSON();

npm install moment

const moment = require('moment'); 
  
let readingTime = moment.duration(10, 'minutes'); 
let lastUpdated = moment.duration(-9, 'months'); 
  
let blogPost = { 
    title: "Blog One", 
    readingTime: readingTime.toJSON(), 
    lastUpdated: lastUpdated.toJSON() 
} 
  
console.log(JSON.stringify(blogPost));

{
    "title": "Blog One",
    "readingTime": "PT10M",
    "lastUpdated": "-P9M"
}

const moment = require('moment'); 
  
let datetime =  
    moment.duration({months: 5, days: 2, hours: 4, seconds: 1}); 
let time =  
    moment.duration({hours: 5, minutes: 6, seconds: 55}); 
let date =  
    moment.duration({years: 10, months: 5, days: 10}); 
  
let exampleJSON = { 
    durationA: datetime.toJSON(), 
    durationB: time.toJSON(), 
    durationC: date.toJSON() 
} 
  
console.log(JSON.stringify(exampleJSON));

{
    "durationA": "P5M2DT4H1S",
    "durationB": "PT5H6M55S",
    "durationC": "P10Y5M10D"
}