toISOString with timezone support

Local ISO String for Date

Date.prototype.toLocalISOString = function(){
	// ISO 8601
	var d = this
		, pad = function (n){return n<10 ? '0'+n : n}
		, tz = d.getTimezoneOffset() //mins
		, tzs = (tz>0?"-":"+") + pad(parseInt(tz/60))
	
	if (tz%60 != 0)
		tzs += pad(tz%60)
	
	if (tz === 0) // Zulu time == UTC
		tzs = 'Z'
		
	 return d.getFullYear()+'-'
	      + pad(d.getMonth()+1)+'-'
	      + pad(d.getDate())+'T'
	      + pad(d.getHours())+':'
	      + pad(d.getMinutes())+':'
	      + pad(d.getSeconds()) + tzs
}

Doesn't work well for timezones ahead of zulu. I.e. tz < 0. Here's a fix

// ISO8601 in local time zone
var localISOString = function() {

    var d = new Date()
        , pad = function (n){return n<10 ? '0'+n : n;}
        , tz = d.getTimezoneOffset() // mins
        , tzs = (tz>0?"-":"+") + pad(parseInt(Math.abs(tz/60)));

    if (tz%60 != 0)
        tzs += pad(Math.abs(tz%60));

    if (tz === 0) // Zulu time == UTC
        tzs = 'Z';

     return d.getFullYear()+'-'
          + pad(d.getMonth()+1)+'-'
          + pad(d.getDate())+'T'
          + pad(d.getHours())+':'
          + pad(d.getMinutes())+':'
          + pad(d.getSeconds()) + tzs;
};

I stumbled across this while needing something like it for my personal project. Here's a much simpler one using ES6.

Date.prototype.toLocalISOString = function () {
    function pad(number) { return ('' + number).padStart(2, '0') }
    return `${this.getFullYear()}-${pad(this.getMonth() + 1)}-${pad(this.getDate())}T${pad(this.getHours())}:${pad(this.getMinutes())}:${pad(this.getSeconds())}`
}

This version does not append the time zone, as I don't need that for my project, but it should be quite easy to add support to it.