simple request function

request.js

function request(method, path, body, headers, ready) {
  var xhr = new XMLHttpRequest
    , zone

  if(typeof headers === 'function') {
    ready = headers
    headers = {}
  } else if(typeof body === 'function') {
    ready = body
    body = null
  }

  headers = headers || {}

  xhr.onreadystatechange = on_state_change(xhr, ready)
  xhr.open(method, path, true)

  for(var key in headers) {
    xhr.setRequestHeader(headers[key])
  }

  xhr.send(body || null)

  return xhr
}

function on_state_change(xhr, done) {
  return function() {
    var parsed

    if(xhr.readyState !== 4) {
      return
    }

    var is_json = /json/.test(xhr.getResponseHeader('Content-Type')) ||
        /json/.test(xhr.getResponseHeader('content-type'))

    try {
      if(xhr.status < 200 || xhr.status > 299) {
        throw new Error('xhr ' + xhr.status + ' ' + xhr.responseText)
      }

      parsed =
        xhr.responseType ? xhr.response :
        is_json ? JSON.parse(xhr.responseText) :
        xhr.responseText
    } catch(e) {
      e.xhr = xhr

      return done(e)
    }

    done(null, parsed)
  }
}

request(String:method, String:path, [Object:headers, [String:body,]] Function:ready) -> xhr