code: function Predator(options) {
    if (!(this instanceof Predator)) {
      return new Predator(options);
    }
  
    if (!options || !options.app) {
      throw new Error('options.app is required');
    }
  
    // 主目录
    this.home = pathFn.resolve(options.home || '.');
  
    // app
    this.app = options.app;
  
    // build 目录
    this.buildDir = pathFn.resolve(options.buildDir || './public');
  }
docs: Preadtor class def
  
  options
  - home: 主目录
  - app: koa app
  - buildDir: build static files