How to output date in javascript in ISO 8601 without milliseconds and with Z

Simple way:

console.log( new Date().toISOString().split('.')[0]+"Z" );

Use slice to remove the undesired part

var now = new Date();
alert( now.toISOString().slice(0,-5)+"Z");

This is the solution:

var now = new Date(); 
var str = now.toISOString();
var res = str.replace(/\.[0-9]{3}/, '');
alert(res);

Finds the . (dot) and removes 3 characters.

http://jsfiddle.net/boglab/wzudeyxL/7/

You can use a combination of split() and shift() to remove the milliseconds from an ISO 8601 string:

let date = new Date().toISOString().split('.').shift() + 'Z';

console.log(date);

or probably overwrite it with this? (this is a modified polyfill from here)

function pad(number) {
  if (number < 10) {
    return '0' + number;
  }
  return number;
}

Date.prototype.toISOString = function() {
  return this.getUTCFullYear() +
    '-' + pad(this.getUTCMonth() + 1) +
    '-' + pad(this.getUTCDate()) +
    'T' + pad(this.getUTCHours()) +
    ':' + pad(this.getUTCMinutes()) +
    ':' + pad(this.getUTCSeconds()) +
    'Z';
};