Add multiple people using Javascript Client Object Model

Question

I am trying to add multiple people to a SP column of type Person/Group i.e. people picker. I am able
to add one successfully using their userId, but HAVE no clue how to do that for multiple people. Here is the code for one user:
function UserDrop(e, toElement, listGuid, columnName) {
//EcmaScript Client Object Model
var ctx = new SP.ClientContext.get_current();
var list = ctx.get_web().get_lists().getById(listGuid);
var item = list.getItemById(elementId);
//columnName is of type person/group and I am adding user //whose userId is 7
item.set_item(columnName, 7);
item.update();
// asynchronous call
ctx.executeQueryAsync(
function () { toElement.innerHTML = userLinkHtml; },
function () {alert ("Error")}
return false;
This works great and I can add user whose userId is 7, however I want to add multiple people like let's say users of user Ids 7 and 8. 
Any ideas or help will be greatly appreciated. 
There is a thread on this one but that's from .net COM which could accessed here: http://social.msdn.microsoft.com/Forums/en-US/sharepoint2010general/thread/5183e87c-ee1d-4594-9492-0dfdf6616cce
7929

Answer 1

Hi ,
Can somebody let me know how the same(assigning the array values to lookup value field) can be achieved with multi-select lookup value. SP.FieldLookUpValue do not have any such methods like fromUser. Please help. Please find my code block below
clientContext = new SP.ClientContext.get_current();
if (this.clientContext != undefined && clientContext != null) {
var webSite = clientContext.get_web();
oList = webSite.get_lists().getByTitle("Add New User");
$.urlParam = function(name){
var results = new RegExp('[\\?&]' + name + '=([^&#]*)').exec(window.location.href);
return results[1] || 0;
var itemid = parseInt($.urlParam('ID'));
var item = oList.getItemById(itemid);
var users = new Array();
users.push(SP.FieldLookupValue.set_lookupId(1));
users.push(SP.FieldLookupValue.set_lookupId(2));
item.set_item('Responsibility', users);
item.update();
clientContext.executeQueryAsync(Function.createDelegate(this, this.success), Function.createDelegate(this, this.failed));
also i cant use managed client object model.. so pls let me know how to achieve the same using javascript client object model
Ranjani.R