lib/Request.js
function genStringify(options) {
  var stringifyFn;
  if (options.headers['Content-Type'] &&
    options.headers['Content-Type'].toLowerCase() === 'application/x-www-form-urlencoded') {
    stringifyFn = querystring.stringify;
  } else {
    switch (options.method.toUpperCase()) {
      case 'POST':
      case 'PUT':
        stringifyFn = JSON.stringify;
        break;
    }
  }
  return stringifyFn;
}
function genStringify(options) {
  var stringifyFn;
  if (options.headers['Content-Type'] &&
    options.headers['Content-Type'].toLowerCase() === 'application/x-www-form-urlencoded') {
    stringifyFn = querystring.stringify;
  } else {
    switch (options.method.toUpperCase()) {
      case 'POST':
      case 'PUT':
        stringifyFn = JSON.stringify;
        break;
    }
  }
  return stringifyFn;
}
yhsd 接口返回的请求量 header 
stringify 参数
@param options
@returns {*}