code: function onPage(output, page) {
      var file = page.getFile();
      var readme = output.getBook().getReadme().getFile();
  
      return Modifiers.modifyHTML(page, getModifiers(output, page))
      .then(function(resultPage) {
          // Generate the JSON
          var json = JSONUtils.encodeBookWithPage(output.getBook(), resultPage);
  
          // Delete some private properties
          delete json.config;
  
          // Specify JSON output version
          json.version = JSON_VERSION;
  
          // File path in the output folder
          var filePath = file.getPath() == readme.getPath()? 'README.json' : file.getPath();
          filePath = PathUtils.setExtension(filePath, '.json');
  
          // Write it to the disk
          return writeFile(
              output,
              filePath,
              JSON.stringify(json, null, 4)
          );
      });
  }
docs: Write a page as a json file
  
  @param {Output} output
  @param {Page} page