date-format.js

function ensureFormat(e) {
	var evt = e || window.event;
	var field = evt.target || evt.srcElement;
	var format = /^\d{1,2}\/\d{1,2}\/\d{2}\/$/;
	var dateParts = field.value.match(format);
	var m, d, y, century;
	
	if (!dateParts) {
		return true;
	}
	
	m = +dateParts[0];
	d = +dateParts[1];
	y = +dateParts[2];

	century = parseInt((new Date().getFullYear()) / 100) * 100;
	
	y += (y < 100) ? ((y < 30) ? century : century - 100) : 0;
	
	field.value = m + "/" + d + "/" + y;

	return true;
	
}