Get all user names instead of User ID from a List using Rest API SharePoint 2013

Use the below code to get user name directly from a list instead of getting a user ID.

Using $expand OData operator you can specify that the request returns projected fields from other lists and the values of lookups.

function getAllUserNames()
{
var deferred = $.Deferred();
var arrayContractOwner = new Array(); // this array to get all user names from list
    var serverUrl = _spPageContextInfo.webAbsoluteUrl;
    var ListNameUrl = String.format("{0}/_api/web/lists/getbytitle('ListName')/items?$select=UserColumnName/Name,UserColumnName/Title&$expand=UserColumnName/Id",serverUrl);

                 
    $.ajax({
                    url: ListNameUrl,
                    type: "GET",
                    headers: {"Accept": "application/json;odata=verbose"},
                    cache:false,              
                    success: function(data)
                    {  
                    var test = data;                      
                   $(data.d.results).each(function(){
                                var UserName = this.UserColumnName.Title;
                              if($.inArray(UserName, arrayContractOwner)==-1)//check userName not present in this array & insert unique names
                              {
                              arrayContractOwner.push(UserName);
                              }
                   });
                   deferred.resolve();
                    },
                    error: function(err)
                    {
                            alert("Request failed :"+JSON.stringify(err));
                    }
    });
    return deferred.promise();
}




Please refer this link for more details Link1