function autoExpand (field) {
	xpos=window.scrollX;
	ypos=window.scrollY;

	field.style.height = 'inherit';

	var computed = window.getComputedStyle(field);

	var height = parseInt(computed.getPropertyValue('border-top-width'), 10)
	+ parseInt(computed.getPropertyValue('padding-top'), 10)
	+ field.scrollHeight
	+ parseInt(computed.getPropertyValue('padding-bottom'), 10)
	+ parseInt(computed.getPropertyValue('border-bottom-width'), 10)
	+ 32;

	field.style.height = height + 'px';

	window.scrollTo(xpos,ypos);
};

document.addEventListener('input', function (event) {
	if (event.target.tagName.toLowerCase() !== 'textarea') return;
	autoExpand(event.target);
}, false);