angularProject/app/directives/scroll-to-top.js

app.directive('scrollTop', [function() {
  let link = function(scope, element, attrs) {

    window.top = {};
    var sc = window.top;
    sc.time = 12; // время прокручивания
    sc.goTop = function (time, acceleration) {
    	acceleration = acceleration || 0.1;
    	time = time || sc.time;
    	var dx = 0;
    	var dy = 0;
    	var bx = 0;
    	var by = 0;
    	var wx = 0;
    	var wy = 0;
    	if (document.documentElement) {
    		dx = document.documentElement.scrollLeft || 0;
    		dy = document.documentElement.scrollTop || 0;
    	}
    	if (document.body) {
    		bx = document.body.scrollLeft || 0;
    		by = document.body.scrollTop || 0;
    	}
    	var wx = window.scrollX || 0;
    	var wy = window.scrollY || 0;
    	var x = Math.max(wx, Math.max(bx, dx));
    	var y = Math.max(wy, Math.max(by, dy));
    	var speed = 1 + acceleration;
    	window.scrollTo(Math.floor(x / speed), Math.floor(y / speed));
    	if(x > 0 || y > 0) {
    		var invokeFunction = "window.top.goTop("+ time +")"
    		window.setTimeout(invokeFunction, time);
    	}
    	return false;
    }

    sc.showHide = function (){
    	var a = document.getElementById('gotop');
      a.onclick = function(e){ e.preventDefault(); window.top.goTop(); }

    	var stop = (document.body.scrollTop || document.documentElement.scrollTop);
    	if( stop > 200 ){
    		a.style.display = 'block';
    		sc.smoothopaque(a, 'show', 30, false);
    	} else {
    		sc.smoothopaque(a, 'hide', 30, function(){a.style.display = 'none';});
    	}
    	return false;
    }
    // Плавная смена прозрачности
    sc.smoothopaque = function (el, todo, speed, endFunc){
    	var
    	startop = Math.round( el.style.opacity * 100 ),
    	op = startop,
    	endop = (todo == 'show') ? 100 : 0;
    	clearTimeout( window['top'].timeout );
    	window['top'].timeout = setTimeout(slowopacity, 20);

    	function slowopacity(){
    		if( startop < endop ){
    			op += 5;
    			if( op < endop )
    				window['top'].timeout = setTimeout(slowopacity, speed);
    			else
    				(endFunc) && endFunc();
    		}
    		else {
    			op -= 5;
    			if( op > endop ){
    				window['top'].timeout = setTimeout(slowopacity, speed);
    			}
    			else
    				(endFunc) && endFunc();
    		}
    		// установка opacity
    		el.style.opacity = (op/100);
    		el.style.filter = 'alpha(opacity=' + op + ')';
    	}
    }
    if (window.addEventListener){
    	window.addEventListener("scroll", sc.showHide, false);
    	window.addEventListener("load", sc.showHide, false);
    }
    else if (window.attachEvent){
    	window.attachEvent("onscroll", sc.showHide);
    	window.attachEvent("onload", sc.showHide);
    }
  }
  return {
    restrict: 'E',
    templateUrl: './app/views/scrollToTop.html',
    link: link
  }
}]);