How do I index by multiple items in an Array or Object using JavaScript/jQuery?

Create a constructor function vis-à-vis class that encapsulates this data, and you can ask it to find users by title, or id. To do a quick lookup, you can create two lookup tables - one for id, and another for title. Assuming a decent hash implementation, the lookups can be done in O(1) on the average. The initial computation is O(n), but lookups are faster. Also it uses slightly more space because we are creating two additional maps. For 1000 objects, that is not a problem. Again, if you will be doing a lot more lookups, this approach will be much faster.

Here's a simple implementation.

function Users(users) {
    this.idMap = {};
    this.titleMap = {};
    this.users = users;
    var me = this;

    users.forEach(function(user) {
        this.idMap[user.Id] = this.idMap[user.Id] || [];
        this.idMap[user.Id].push(user);

        this.titleMap[user.Title] = this.titleMap[user.Title] || [];
        this.titleMap[user.Title].push(user);
    }.bind(this));
}

Users.prototype.findByTitle = function(title) {
    return this.titleMap[title];
};

Users.prototype.findById = function(id) {
    return this.idMap[id];
};

To use it, create an object of Users passing it the AJAX response, and then query it using the findById and findByTitle methods.

var users = new Users(responseData);
users.findById("1");
users.findByTitle("SomeTitle");

Checkout a working example.

If you have control over the data returned, it's better if you produce it with the following format:

var allUsers=[
{"005400000001234567":{
    Name:"User Name",
    FirstName:"User",
    LastName:"Name",`
    Title:"Manager"
}} 
,{"005400000001234568":{
    Name:"User2 Name2",
    FirstName:"User2",
    LastName:"Name2",
    Title:"Manager2"
}} 
/*..etc.. */
];

This way you avoid the loop ($(result).each()) inside GetAllUsers (which builds the array above). The search by title can be performed efficiently by building a second array of the form:

var byTitle=["title1":[0,1], "title1":[0,1], /*etc*/];

As you see, each title has a list of indexes to allUsers. Then you simply do:

var allManagers = [];
for(var i in byTitle["Manager"]) allManagers.push(allUsers[i]);

I think this should work. I really can't test it without your data.

function GetAllUsers()
{

AllUsersById = new Object();
AllUsersByType = new Object();

MyClass.MyAjaxMethod(function(result,event) {
    if(result) { 
        j$(result).each(function(index,item)
        {
            // By Id
            AllUsersById[item.Id] = item;

            // By Type
            if (!AllUsersByTitle[item.Title]) {
                AllUsersByTitle[item.Title] = new Array();
            }

            AllUsersByType[item.type].push() = item;
        });


    }
});
}