How to use the @lykmapipo/mongoose-common.isInstance function in @lykmapipo/mongoose-common

function findExisting(next) {
        if (isInstance(model)) {
          next(null, model);
        } else {
          // prepare find query
          const findQuery = Model.findById(model._id);

          // if filter
          if (model.filter) {
            findQuery.where(model.filter);
          }

          findQuery.orFail().exec(next); //TODO use getById
        }
      },

const updatesFor = (id, updates) => {
  // normalize id
  const options = _.isPlainObject(id) ? id : { _id: id };

  // ignore self instance updates
  if (isInstance(updates) && updates._id === options._id) {
    return updates;
  }

  // compute updates
  const changes = mergeObjects(copyInstance(updates), options);
  return changes;
};

const updatesFor = (id, updates) => {
  // normalize id
  const options = _.isPlainObject(id) ? id : { _id: id };

  // ignore self instance updates
  if (isInstance(updates) && updates._id === options._id) {
    return updates;
  }

  // compute updates
  const changes = mergeObjects(copyInstance(updates), options);
  return changes;
};

function afterFindExisting(instance, next) {
        // handle instance
        if (isInstance(model)) {
          model.patch({ updatedAt: new Date() }, next);
        }
        // handle updates
        else {
          delete model._id;
          delete model.id;
          instance.patch(model, next);
        }
      }

function afterFindExisting(instance, next) {
        // handle instance
        if (isInstance(model)) {
          model.put({ updatedAt: new Date() }, next);
        }
        // handle updates
        else {
          delete model._id;
          delete model.id;
          instance.put(model, next);
        }
      }

schema.statics.post = function post(body, done) {

    //instantiate model
    const instance = (
      isInstance(body) ?
      body :
      new this(copyInstance(body))
    );

    //persist model
    instance.post(done);

  };