How to Get your manager with Javascript

You create an instance of a manager object by using PeopleManager class in JSOM SharePoint 2013.
See the sample code below:

//Make sure SP.UserProfiles.js file is loaded before code runs.
SP.SOD.executeOrDelayUntilScriptLoaded(getUserProperties, 'SP.UserProfiles.js');
var userProfileProperties;

function getUserProperties() {

    // get the target users domain name and account name.
    var targetUser = "SomeDomain\\SomeUserName";

    // Get the current client context and PeopleManager instance.
    var clientContext = new SP.ClientContext.get_current();
    var peopleManager = new SP.UserProfiles.PeopleManager(clientContext);

    // Specify the properties to retrieve
    var profilePropertyNames = ["PreferredName", "Department"];
    var userProfilePropertiesForUser = new SP.UserProfiles.UserProfilePropertiesForUser(
            clientContext,
            targetUser,
            profilePropertyNames);

    // Get user profile properties for the target user using the UserProfilePropertyFor method.
    userProfileProperties = peopleManager.getUserProfilePropertiesFor(userProfilePropertiesForUser);

    // Load the UserProfilePropertiesForUser object and send the request.
    clientContext.load(userProfilePropertiesForUser);
    clientContext.executeQueryAsync(onRequestSuccess, onRequestFail);
}

// This function runs if the executeQueryAsync call succeeds.
function onRequestSuccess() {
    var messageText = "\"PreferredName\" property is "
        + userProfileProperties[0];
    messageText += "<br />\"Department\" property is "
        + userProfileProperties[1];
    $get("results").innerHTML = messageText;
}

// This function runs if the executeQueryAsync call fails.
function onRequestFail(sender, args) {
    $get("results").innerHTML = "Error: " + args.get_message();
}

In SharePoint 2010 and 2007, you can use SPServices library.