lib/model.js
function model (doc, fields) {
    if (!(this instanceof model))
      return new model(doc, fields);
    Model.call(this, doc, fields);
  }
function model (doc, fields) {
    if (!(this instanceof model))
      return new model(doc, fields);
    Model.call(this, doc, fields);
  }
function model ( doc , fields ) { if ( ! ( this instanceof model ) ) return new model ( doc , fields ) ; Model . call ( this , doc , fields ) ; }
generate new class
generate new class