[javascript] How do I format a date as ISO 8601 in moment.js?

This docs mention moment.ISO_8601 as a formatting option (from 2.7.0 - http://momentjs.com/docs/#/parsing/special-formats/), but neither of these work (even 2.7.0):

var date = moment();
date.format(moment.ISO_8601); // error
moment.format(date, moment.ISO_8601); // error

(http://jsfiddle.net/b3d6uy05/1/)

How can I get an ISO 8601 from moment.js?

var date = moment(new Date(), moment.ISO_8601);
console.log(date);

If you just want the date portion (e.g. 2017-06-27), and you want it to work regardless of time zone and also in Arabic, here is code I wrote:

function isoDate(date) {
    if (!date) {
        return null
    }
    date = moment(date).toDate()

    // don't call toISOString because it takes the time zone into
    // account which we don't want.  Also don't call .format() because it
    // returns Arabic instead of English

    var month = 1 + date.getMonth()
    if (month < 10) {
        month = '0' + month
    }
    var day = date.getDate()
    if (day < 10) {
        day = '0' + day
    }
    return date.getFullYear() + '-' + month + '-' + day
}

var x = moment();

//date.format(moment.ISO_8601); // error

moment("2010-01-01T05:06:07", ["YYYY", moment.ISO_8601]);; // error
document.write(x);

Also possible with vanilla JS

new Date().toISOString() // "2017-08-26T16:31:02.349Z"

When you use Mongoose to store dates into MongoDB you need to use toISOString() because all dates are stored as ISOdates with miliseconds.

moment.format() 

2018-04-17T20:00:00Z

moment.toISOString() -> USE THIS TO STORE IN MONGOOSE

2018-04-17T20:00:00.000Z

Answer in 2020 (Includes Timezone Support)

The problem we were having is that, by default, ISOStrings aren't localized to your timezone. So, this is kinda hacky, but here's how we ended up solving this issue:

/** Imports Moment for time utilities. */
const moment = require("moment-timezone")
moment().tz("America/Chicago").format()

//** Returns now in ISO format in Central Time */
export function getNowISO() {
  return `${moment().toISOString(true).substring(0, 23)}Z`
}

This will leave you with an exact ISO-formatted, localized string.

Important note: Moment now suggests using other packages for new projects.

Use format with no parameters:

var date = moment();
date.format(); // "2014-09-08T08:02:17-05:00"

(http://jsfiddle.net/8gvhL1dz/)