Getting current login details using javascript

<script type="text/javascript">

ExecuteOrDelayUntilScriptLoaded(init,'sp.js');

var currentUser;

function init(){

    this.clientContext = new SP.ClientContext.get_current();

    this.oWeb = clientContext.get_web();

    currentUser = this.oWeb.get_currentUser();

    this.clientContext.load(currentUser);

    this.clientContext.executeQueryAsync(Function.createDelegate(this,this.onQuerySucceeded), Function.createDelegate(this,this.onQueryFailed));

}

function onQuerySucceeded() {

    alert(currentUser.get_loginName());

    alert(currentUser.get_id());

    alert(currentUser.get_title());

    alert(currentUser.get_email());

}

function onQueryFailed(sender, args) {

    alert('Request failed. \nError: ' + args.get_message() + '\nStackTrace: ' + args.get_stackTrace());

}

</script>