Function takes in an element to find the top of it's position, also the speed (in milliseconds) at which the scroll should occur. Defaults to the top of the document at a "slow" tempo.

jquery-scroll-to-top.js

var scrollToTop = function(el, speed) {
	/**
	 * Function takes in the element to scroll to, as well as
	 * the speed in which the document should scroll animate to the top.
	 *
	 * Default is window top, and slow (respectively). Time (in milliseconds is allowed)
	 */
	"use strict";
	var position;

	if(el === undefined){
		position = 0;
	} else {
		position = $(el).offset().top;
	}
	if(speed === undefined) speed = "slow"

	$("html, body").animate({ scrollTop: position }, speed);
};