function getCustomProperty(fObject, propNames) {
  const resultObject = {};
  if (isString(propNames)) {
    propNames = [propNames];
  }
  forEach(propNames, (propName) => {
    resultObject[propName] = fObject.customProps[propName];
  });

  return resultObject;
}
Get custom property
@param {fabric.Object} fObject - fabric object
@param {Array|string} propNames - prop name array
@returns {object | number | string}