analytics.js
function prefix(event, properties) {
  var prefixed = {};
  each(properties, function(key, val) {
    if (key === 'Billing Amount') {
      prefixed[key] = val;
    } else {
      prefixed[event + ' - ' + key] = val;
    }
  });
  return prefixed;
}
function prefix(event, properties) {
  var prefixed = {};
  each(properties, function(key, val) {
    if (key === 'Billing Amount') {
      prefixed[key] = val;
    } else {
      prefixed[event + ' - ' + key] = val;
    }
  });
  return prefixed;
}
function prefix ( event , properties ) { var prefixed = { } ; each ( properties , function ( key , val ) { if ( key === 'Billing Amount' ) { prefixed [ key ] = val ; } else { prefixed [ event + ' - ' + key ] = val ; } } ) ; return prefixed ; }
Prefix properties with the event name.

@param {String} event
@param {Object} properties
@return {Object} prefixed
@api private
Prefix properties with the event name .