code: function format (args) {
    return args.map((v) => {
      const type = Object.prototype.toString.call(v)
      if (type.toLowerCase() === '[object object]') {
        v = JSON.stringify(v)
      }
      else {
        v = String(v)
      }
      return v
    })
  }
docs: Convert all log arguments into primitive values.
  @param  {array} args
  @return {array}
   /* istanbul ignore next