code: @GwtIncompatible("Unnecessary")
    JsonFileSpec createJsonFile(B options, String outputMarker, Function<String, String> escaper)
        throws IOException {
      Appendable jsOutput = new StringBuilder();
      writeOutput(
          jsOutput, compiler, (JSModule) null, config.outputWrapper,
          outputMarker, escaper);
  
      JsonFileSpec jsonOutput = new JsonFileSpec(jsOutput.toString(),
          Strings.isNullOrEmpty(config.jsOutputFile) ?
              "compiled.js" : config.jsOutputFile);
  
      if (!Strings.isNullOrEmpty(options.sourceMapOutputPath)) {
        StringBuilder sourcemap = new StringBuilder();
        compiler.getSourceMap().appendTo(sourcemap, jsonOutput.getPath());
        jsonOutput.setSourceMap(sourcemap.toString());
      }
  
      return jsonOutput;
    }
docs: Save the compiler output to a JsonFileSpec to be later written to stdout