sharepoint csom get user

sp_getUser_csom.js

var context;
var web;
var user;
 
// This code runs when the DOM is ready and creates a context object which is needed to use the SharePoint object model
$(document).ready(function () {
    context = SP.ClientContext.get_current();
    web = context.get_web();
 
    getUserName();
});
 
// This function prepares, loads, and then executes a SharePoint query to get the current users information
function getUserName() {
    user = web.get_currentUser();
    context.load(user);
    context.executeQueryAsync(onGetUserNameSuccess, onGetUserNameFail);
}
 
// This function is executed if the above OM call is successful
// It replaces the contents of the 'helloString' element with the user name
function onGetUserNameSuccess() {
    $('#message').text('Hello ' + user.get_title());
}
 
// This function is executed if the above call fails
function onGetUserNameFail(sender, args) {
    alert('Failed to get user name. Error:' + args.get_message());
}