How do I output an ISO 8601 formatted string in JavaScript?

Question

There is already a function called toISOString():

var date = new Date();
date.toISOString(); //"2011-12-19T15:28:46.493Z"

If, somehow, you're on a browser that doesn't support it, I've got you covered:

if (!Date.prototype.toISOString) {
  (function() {

    function pad(number) {
      var r = String(number);
      if (r.length === 1) {
        r = '0' + r;
      }
      return r;
    }

    Date.prototype.toISOString = function() {
      return this.getUTCFullYear() +
        '-' + pad(this.getUTCMonth() + 1) +
        '-' + pad(this.getUTCDate()) +
        'T' + pad(this.getUTCHours()) +
        ':' + pad(this.getUTCMinutes()) +
        ':' + pad(this.getUTCSeconds()) +
        '.' + String((this.getUTCMilliseconds() / 1000).toFixed(3)).slice(2, 5) +
        'Z';
    };

  }());
}

console.log(new Date().toISOString())

See the last example on page https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference:Global_Objects:Date:

/* Use a function for the exact format desired... */
function ISODateString(d) {
    function pad(n) {return n<10 ? '0'+n : n}
    return d.getUTCFullYear()+'-'
         + pad(d.getUTCMonth()+1)+'-'
         + pad(d.getUTCDate())+'T'
         + pad(d.getUTCHours())+':'
         + pad(d.getUTCMinutes())+':'
         + pad(d.getUTCSeconds())+'Z'
}

var d = new Date();
console.log(ISODateString(d)); // Prints something like 2009-09-28T19:03:12Z

Almost every to-ISO method on the web drops the timezone information by applying a convert to "Z"ulu time (UTC) before outputting the string. Browser's native .toISOString() also drops timezone information.

This discards valuable information, as the server, or recipient, can always convert a full ISO date to Zulu time or whichever timezone it requires, while still getting the timezone information of the sender.

The best solution I've come across is to use the Moment.js javascript library and use the following code:

To get the current ISO time with timezone information and milliseconds

now = moment().format("YYYY-MM-DDTHH:mm:ss.SSSZZ")
// "2013-03-08T20:11:11.234+0100"

now = moment().utc().format("YYYY-MM-DDTHH:mm:ss.SSSZZ")
// "2013-03-08T19:11:11.234+0000"

now = moment().utc().format("YYYY-MM-DDTHH:mm:ss") + "Z"
// "2013-03-08T19:11:11Z" <- better use the native .toISOString() 

To get the ISO time of a native JavaScript Date object with timezone information but without milliseconds

var current_time = Date.now();
moment(current_time).format("YYYY-MM-DDTHH:mm:ssZZ")

This can be combined with Date.js to get functions like Date.today() whose result can then be passed to moment.

A date string formatted like this is JSON compilant, and lends itself well to get stored into a database. Python and C# seem to like it.

The question asked was ISO format with reduced precision. Voila:

 new Date().toISOString().slice(0, 19) + 'Z'
 // '2014-10-23T13:18:06Z'

Assuming the trailing Z is wanted, otherwise just omit.