Scrolls form inputs when they are hidden by a fixed header or footer

Unhide Inputs

// Make sure focused elements aren't hidden by fixed positioned header or footer
function unhideInput(formelement) {
	formelement.onfocus = function () {
		var paddingheight = 30;
		var headerheight = document.getElementsByTagName('header')[0].offsetHeight;
		var footerheight = document.getElementsByTagName('footer')[document.getElementsByTagName('footer').length - 1].offsetHeight;
		var viewportheight = window.innerHeight;
		var elementpos = this.getBoundingClientRect();

		if ((elementpos.top <= (headerheight + paddingheight)) || (elementpos.bottom >= (viewportheight - footerheight))) {
			this.scrollIntoView(true);
			window.scrollBy(0, Math.round(viewportheight / 2));
		}
	}
}

var htmltag = document.getElementsByTagName('html')[0];
if (! /iOS/i.test(htmltag.className)) {
	var forminputs = document.getElementsByTagName('input');
	var formtextareas = document.getElementsByTagName('textarea');
	var formbuttons = document.getElementsByTagName('button');

	for (var i = forminputs.length - 1; i >= 0; i--) {
		forminputs[i].addEventListener('focus', unhideInput(forminputs[i]), false);
	};

	for (var i = formtextareas.length - 1; i >= 0; i--) {
		formtextareas[i].addEventListener('focus', unhideInput(formtextareas[i]), false);
	};

	for (var i = formbuttons.length - 1; i >= 0; i--) {
		formbuttons[i].addEventListener('focus', unhideInput(formbuttons[i]), false);
	};
}