code: function realRequirPath(filePath) {
    // console.log('realRequirPath:filePath: ' + filePath);
    var jsFilePath = filePath + '.js';
    if (fs.existsSync(filePath)) {
      if (fs.statSync(filePath).isDirectory()) {
        jsFilePath = filePath + '.js';
        if (fs.existsSync(jsFilePath)) {
          return jsFilePath;
        } else {
          jsFilePath = path.join(filePath, 'index.js');
        }
        // console.log('realRequirPath:jsFilePath: ' + jsFilePath);
      } else if (fs.statSync(filePath).isFile()) {
        return filePath;
      } else {
        return null;
      }
    } else {
      jsFilePath = filePath + '.js';
      // console.log('realRequirPath:filePath: ' + filePath);
    }
  
    if (fs.existsSync(jsFilePath)) {
      // console.log('realRequirPath:filePath: ' + filePath);
      return jsFilePath;
    } else {
      return null;
    }
  }
docs: get real required file path
  
  module to module.js or module/index.js
  
  @param filePath
  @returns {*}