nice pattern for jsom async calls

pass the call backs as parameters to the function



function getSiteField(fieldName,success,failure)
{
     var ctx = SP.ClientContext.get_current();
     var rootWeb = ctx.get_site().get_rootWeb();
     var field = rootWeb.get_availableFields().getByInternalNameOrTitle(fieldName);
     ctx.load(field);
     ctx.executeQueryAsync(
         function(){
            success(field)
         },
         failure);
}
SP.SOD.executeFunc('SP.js', 'SP.ClientContext', function() {

   //get Title column and print its properties
   getSiteField('Title',
    function(field){
       //print field properties
       console.log(field.get_title());
       console.log(field.get_internalName());
       console.log(field.get_typeAsString());
       console.log(field.get_description());
    },
    function(sender,args){
       console.log(args.get_message());
    });

});

got it here