document.getElementById("show-menu").onclick=function toggleMenu() {
	if (document.getElementById("menu").className == "menu-up" 
	|| document.getElementById("menu").className == "menu-off") {
		document.getElementById("menu").className = "menu-down";
		document.getElementById("wrapper").className = "wrapper-down";
	} else {
		document.getElementById("menu").className = "menu-up";
		document.getElementById("wrapper").className = "wrapper-up";
	}
} //this function toggles the menu and wrapper between up and down positions


var menuLinks = document.getElementsByClassName("menu-link"); //An array containing the three menu links.

var clickedSection; // Will store the section ID after a link is clicked
var timer; // Stores the interval which makes the scrolling possible


var topLinks = document.getElementsByClassName("top"); // Contains the 'return to top links'
var fromTop; //Will store how far from the top the scrollbar is
var vOffset; //will store how far from the top an element is.
var scrollSpeed = 20; //This variable alters the scroll speed


for (i=0; i<=3; i++) {
	if (menuLinks[i]) {
		menuLinks[i].addEventListener("click", function() {
			clickedSection = this.id.replace("link",""); //Saves the name of the section the user has selected			
			menuSelect();
		});
	}
}



function menuSelect() {
	document.getElementById("menu").className = "menu-off";
	document.getElementById("wrapper").className = "wrapper-off";

	vOffset = document.getElementById(clickedSection).offsetTop; //Calculates how far in pixels the selected element is from the top
	fromTop = document.body.scrollTop; //Calculates how far in pixels the current scroll position is from the top
	timer = setInterval(scrollDown, 5); //calls the function scrollDown once every 5 milliseconds until clearInterval is applied
} 


for (i=0; i<topLinks.length; i++) {
	topLinks[i].addEventListener("click", function() {
		fromTop = document.body.scrollTop; //Calculates how far in pixels the current scroll position is from the top
		timer = setInterval(scrollUp, 5); //calls the function scrollUp once every 5 milliseconds until clearInterval is applied
	})
}

function scrollUp(){
	window.scrollBy(0, -scrollSpeed); //Scrolls up by the number of pixes specified by scrollSpeed
	fromTop -= scrollSpeed; //Updates fromTop to the current position
	if (fromTop <= 0) {
		clearInterval(timer);
	} //stops scrolling when top is reached
}

function scrollDown(){
	window.scrollBy(0, scrollSpeed); //Scrolls down by the number of pixes specified by scrollSpeed
	fromTop += scrollSpeed; //Updates fromTop to the current position
	if (fromTop >= vOffset) {
		clearInterval(timer);
	} //stops scrolling when selected element is reached

}