code: function isCallback(arg){
      if(typeof arg === 'function'){
          let str = String(arg);
          if(/^function\*?(\s+(done|callback|cb))\s*\(/.test(str) ||
              /^function\*?(\s+\w+)?\s*\(\s*(error|err|e)\s*(,|\))/i.test(str)){
              return true;
          }
      }
      return false;
  }
docs: check callback