How to get 30 days prior to current date?

Question

Try this

var today = new Date()
var priorDate = new Date().setDate(today.getDate()-30)

As noted by @Neel, this method returns in Javascript Timestamp format. To convert it back to date object, you need to pass the above to a new Date object; new Date(priorDate).

Try using the excellent Datejs JavaScript date library (the original is no longer maintained so you may be interested in this actively maintained fork instead):

Date.today().add(-30).days(); // or...
Date.today().add({days:-30});

[Edit]

See also the excellent Moment.js JavaScript date library:

moment().subtract(30, 'days'); // or...
moment().add(-30, 'days');

Here's an ugly solution for you:

var date = new Date(new Date().setDate(new Date().getDate() - 30));

startDate = new Date(today.getTime() - 30*24*60*60*1000);

The .getTime() method returns a standard JS timestamp (milliseconds since Jan 1/1970) on which you can use regular math operations, which can be fed back to the Date object directly.

Get next 30th day from today

let now = new Date()
console.log('Today: ' + now.toUTCString())
let next30days = new Date(now.setDate(now.getDate() + 30))
console.log('Next 30th day: ' + next30days.toUTCString())

Get last 30th day form today

let now = new Date()
console.log('Today: ' + now.toUTCString())
let last30days = new Date(now.setDate(now.getDate() - 30))
console.log('Last 30th day: ' + last30days.toUTCString())

Javascript can handle it without any external libraries.

var today = new Date();
var dateLimit = new Date(new Date().setDate(today.getDate() - 30));

document.write(today + "<br/>" + dateLimit)