/**
* Set a cookie
* @param string cookie name
* @param string cookie value
* @param string cookie expiration counter in days
* @param string cookie path
* @param string cookie domain
* @param bool secure?
*/
function setCookie( name, value, expires, path, domain, secure ) {
	var today = new Date();
	today.setTime( today.getTime() );
	if ( expires ) {
		expires = expires * 1000 * 60 * 60 * 24;
	}
	var expires_date = new Date( today.getTime() + (expires) );
	document.cookie = name+"="+escape( value ) +
		( ( expires ) ? ";expires="+expires_date.toGMTString() : "" ) +
		( ( path ) ? ";path=" + path : "" ) +
		( ( domain ) ? ";domain=" + domain : "" ) +
		( ( secure ) ? ";secure" : "" );
}

/**
* Get a cookie value
* @param string cookie name
*/
function getCookie( name ) {
	var start = document.cookie.indexOf( name + "=" );
	var len = start + name.length + 1;
	if ( ( !start ) && ( name != document.cookie.substring( 0, name.length ) ) ) {
		return null;
	}
	if ( start == -1 ) return null;
	var end = document.cookie.indexOf( ";", len );
	if ( end == -1 ) end = document.cookie.length;
	return unescape( document.cookie.substring( len, end ) );
}

/**
* Remebers form inputs after you fill them in
* @param string ID of the form you want inputs remembered for
*/
function rememberFormInputs(form_id) {
	// get a reference to the form element with id 'form_test'
	var form = document.getElementById(form_id);
	// get all child input elements of the form
	var els = document.getElementsByTagName('input');
	// iterate through all form child input elements
	for (var i = 0; i < els.length; i++) {
		// this is the element with index of i
		var el = els.item(i);
		// make sure this is a text input field
		if (el.type == 'text') {
		
			// event handler to catch onblur events
			// it sets the cookie values each time you move out of an input field
			el.onblur = function() {
				// this is the name of the input field
				var name = this.name;
				// this is the value of the input field
				var value = this.value;
				// set the cookie
				setCookie( form_id + name, value);
				alert('setCookie: '+name + ' = '+value);
			};
			
			// this inserts all the remembered cookie values into the input fields
			var old_value = getCookie(form_id + el.name);
			if (old_value && old_value != '') {
				alert('old value remembered: '+old_value);
				el.value = old_value;
			}
		}
	}
}

<form id="myform">.... inputs ....</form>

// function will be run after window/document loads
window.onload = function() {
	rememberFormInputs('myform');
}