Get "CreatedBy" and "ModifiedBy" Values From SharePoint
var oCreatedBy = listItem.get_item("Author");
var oModifiedBy = listItem.get_item("Editor");
console.log("Created By: " + oCreatedBy.get_lookupValue() + " Modified By: " + oModifiedBy.get_lookupValue() + "");
var oCreatedBy = listItem.get_item("Author");
var oModifiedBy = listItem.get_item("Editor");
console.log("Created By: " + oCreatedBy.get_lookupValue() + " Modified By: " + oModifiedBy.get_lookupValue() + "");