How to use the @nuxt/utils.urlJoin function in @nuxt/utils

output () {
    const {
      options: { buildDir, router },
      buildOptions: { publicPath }
    } = this.buildContext
    return {
      path: path.resolve(buildDir, 'dist', this.isServer ? 'server' : 'client'),
      filename: this.getFileName('app'),
      futureEmitAssets: true, // TODO: Remove when using webpack 5
      chunkFilename: this.getFileName('chunk'),
      publicPath: isUrl(publicPath) ? publicPath : urlJoin(router.base, publicPath)
    }
  }

constructor(serverContext) {
    super(serverContext)

    const { build: { publicPath }, router: { base } } = this.options
    this.publicPath = isUrl(publicPath) ? publicPath : urlJoin(base, publicPath)
  }