index.js

var queryString = require('query-string')
var setQuery = require('url-set-query')
var assign = require('object-assign')
var ensureHeader = require('./lib/ensure-header.js')

// this is replaced in the browser
var request = require('./lib/request.js')

var mimeTypeJson = 'application/json'
var noop = function () {}

module.exports = xhrRequest
function xhrRequest (url, opt, cb) {
  if (!url || typeof url !== 'string') {
    throw new TypeError('must specify a URL')
  }
  if (typeof opt === 'function') {
    cb = opt
    opt = {}
  }
  if (cb && typeof cb !== 'function') {
    throw new TypeError('expected cb to be undefined or a function')
  }

  cb = cb || noop
  opt = opt || {}

  var defaultResponse = opt.json ? 'json' : 'text'
  opt = assign({ responseType: defaultResponse }, opt)

  var headers = opt.headers || {}
  var method = (opt.method || 'GET').toUpperCase()
  var query = opt.query
  if (query) {
    if (typeof query !== 'string') {
      query = queryString.stringify(query)
    }
    url = setQuery(url, query)
  }

  // allow json response
  if (opt.responseType === 'json') {
    ensureHeader(headers, 'Accept', mimeTypeJson)
  }

  // if body content is json
  if (opt.json && method !== 'GET' && method !== 'HEAD') {
    ensureHeader(headers, 'Content-Type', mimeTypeJson)
    opt.body = JSON.stringify(opt.body)
  }

  opt.method = method
  opt.url = url
  opt.headers = headers
  delete opt.query
  delete opt.json

  return request(opt, cb)
}