ECMA Script : To get the current logged in user information in SharePoint 2010

 
<script language="ecmascript" type="text/ecmascript">
 
    var clientContext = null;
    var oWeb = null;
    var user = null;
 
    function getUserInfo() {
 
        clientContext = new SP.ClientContext.get_current()
        oWeb = clientContext.get_web();
        user = oWeb.get_currentUser();
        clientContext.load(user);
        clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
    }
 
    function onQuerySucceeded() {
        var message = "User Information";
        message += "\n User Name: " + user.get_title();
        message += "\n Login Name: " + user.get_loginName();        
        alert(message);
    }
 
    function onQueryFailed(sender, args) {
        alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
    }
 
</script>
<input id="btnGetUserInfo" onclick="getUserInfo()" type="button" value="Get Current Login User"/>