code: function setWriteHeadHeaders (statusCode) {
    var length = arguments.length
    var headerIndex = length > 1 && typeof arguments[1] === 'string'
      ? 2
      : 1
  
    var headers = length >= headerIndex + 1
      ? arguments[headerIndex]
      : undefined
  
    this.statusCode = statusCode
  
    if (Array.isArray(headers)) {
      // handle array case
      setHeadersFromArray(this, headers)
    } else if (headers) {
      // handle object case
      setHeadersFromObject(this, headers)
    }
  
    // copy leading arguments
    var args = new Array(Math.min(length, headerIndex))
    for (var i = 0; i < args.length; i++) {
      args[i] = arguments[i]
    }
  
    return args
  }
docs: Set headers and other properties on the response object.
  
  @param {number} statusCode
  @private