sharepoint Working with JavaScript Client Object Model (JSOM) Get Current User Information
Example
SP.SOD.executeOrDelayUntilScriptLoaded(showUserInfo,"sp.js");
function showUserInfo(){
var clientContext = new SP.ClientContext();
var user = clientContext.get_web().get_currentUser();
clientContext.load(user);
clientContext.executeQueryAsync(function(){
var details = "ID: "+user.get_id()+"\n"+
"Title: "+user.get_title()+"\n"+
"Login: "+user.get_loginName()+"\n"+
"Email: "+user.get_email();
alert(details);
},function(sender,args){alert(args.get_message());})
}
