Display Form ID Function - Length Is Null

For some reason i'm getting the error of "length is null". Which is from this.
function display_form(id) {
//Create some variables
var html = "";
var container = "form_container";
var menu = load_menu(id, false);

//Get id
for ( var i = 0; i < menu.length; i++ ) {
alert(i);
}

http = getHTTPObject();
http.onreadystatechange = function() {
if ( http.readyState == 4 && http.status == 200 ) {
document.getElementById(container).innerHTML = http.responseText;
} else {
document.getElemenyById(container).innerHTML = "Loading...";
}}
http.open( "GET", "includes/forms.php?form=" + id );
http.send();
//Watch input fields
//login_listener();
}/*

Here is the function:
function load_menu(menu, return_d) {
//Availible menus
var data = [];
data [ 'login' ] = [ 'Login', 'Register', 'Recovery' ];
data [ 'settings' ] = [ 'Profile', 'Account', 'something' ];

if (return_d == false) {
return data[ menu ];
} else {
//Menu container ID's
var cons = Array('menuitem1','menuitem2','menuitem3');

for ( var i = 0; i < cons.length; i++ ) {
document.getElementById(cons[i]).innerHTML += data[ menu ] [ i ];
}}}

Extra info:
id = login
menu = login