code: function (request, callback) {
    const parsed = url.parse(request.url)
    if (!parsed.hostname || !parsed.path) return callback()
  
    const manifest = manifestMap[parsed.hostname]
    if (!manifest) return callback()
  
    const page = backgroundPages[parsed.hostname]
    if (page && parsed.path === `/${page.name}`) {
      // Disabled due to false positive in StandardJS
      // eslint-disable-next-line standard/no-callback-literal
      return callback({
        mimeType: 'text/html',
        data: page.html
      })
    }
  
    fs.readFile(path.join(manifest.srcDirectory, parsed.path), function (err, content) {
      if (err) {
        // Disabled due to false positive in StandardJS
        // eslint-disable-next-line standard/no-callback-literal
        return callback(-6) // FILE_NOT_FOUND
      } else {
        return callback(content)
      }
    })
  }
docs: The chrome-extension: can map a extension URL request to real file path.