OutgoingMessage.prototype.setHeader = function(name, value) {
  if (typeof name !== 'string')
    throw new TypeError('`name` should be a string in setHeader(name, value).');
  if (value === undefined)
    throw new Error('`value` required in setHeader("' + name + '", value).');
  if (this._header)
    throw new Error('Can\'t set headers after they are sent.');
	//...
	```