code: function ExpressHandlebars(config) {
      // Config properties with defaults.
      utils.assign(this, {
          handlebars     : Handlebars,
          extname        : '.handlebars',
          layoutsDir     : undefined, // Default layouts directory is relative to `express settings.view` + `layouts/`
          partialsDir    : undefined, // Default partials directory is relative to `express settings.view` + `partials/`
          defaultLayout  : undefined,
          helpers        : undefined,
          compilerOptions: undefined,
      }, config);
  
      // Express view engine integration point.
      this.engine = this.renderView.bind(this);
  
      // Normalize `extname`.
      if (this.extname.charAt(0) !== '.') {
          this.extname = '.' + this.extname;
      }
  
      // Internal caches of compiled and precompiled templates.
      this.compiled    = Object.create(null);
      this.precompiled = Object.create(null);
  
      // Private internal file system cache.
      this._fsCache = Object.create(null);
  }
docs: -----------------------------------------------------------------------------