text: var support = {
    searchParams: 'URLSearchParams' in self,
    iterable: 'Symbol' in self && 'iterator' in Symbol,
    blob:
      'FileReader' in self &&
      'Blob' in self &&
      (function() {
        try {
          new Blob()
          return true
        } catch (e) {
          return false
        }
      })(),
    formData: 'FormData' in self,
    arrayBuffer: 'ArrayBuffer' in self
  }
  
  function isDataView(obj) {
    return obj && DataView.prototype.isPrototypeOf(obj)
  }
  
  if (support.arrayBuffer) {
    var viewClasses = [
      '[object Int8Array]',
      '[object Uint8Array]',
      '[object Uint8ClampedArray]',
      '[object Int16Array]',
      '[object Uint16Array]',
      '[object Int32Array]',
      '[object Uint32Array]',
      '[object Float32Array]',
      '[object Float64Array]'
    ]
  
    var isArrayBufferView =
      ArrayBuffer.isView ||
      function(obj) {
        return obj && viewClasses.indexOf(Object.prototype.toString.call(obj)) > -1
      }
  }
  
  function normalizeName(name) {
    if (typeof name !== 'string') {
      name = String(name)
    }
    if (/[^a-z0-9\-#$%&'*+.^_`|~!]/i.test(name) || name === '') {
      throw new TypeError('Invalid character in header field name')
    }
    return name.toLowerCase()
  }
  
  function normalizeValue(value) {
    if (typeof value !== 'string') {
      value = String(value)
    }
    return value
  }
  
  // Build a destructive iterator for the value list
  function iteratorFor(items) {
    var iterator = {
      next: function() {
        var value = items.shift()
        return {done: value === undefined, value: value}
      }
    }
  
    if (support.iterable) {
      iterator[Symbol.iterator] = function() {
        return iterator
      }
    }
  
    return iterator
  }
  
  export function Headers(headers) {
    this.map = {}
  
    if (headers instanceof Headers) {
      headers.forEach(function(value, name) {
        this.append(name, value)
      }, this)
    } else if (Array.isArray(headers)) {
      headers.forEach(function(header) {
        this.append(header[0], header[1])
      }, this)
    } else if (headers) {
      Object.getOwnPropertyNames(headers).forEach(function(name) {
        this.append(name, headers[name])
      }, this)
    }
  }
  
  Headers.prototype.append = function(name, value) {
    name = normalizeName(name)
    value = normalizeValue(value)
    var oldValue = this.map[name]
    this.map[name] = oldValue ? oldValue + ', ' + value : value
  }
  
  Headers.prototype['delete'] = function(name) {
    delete this.map[normalizeName(name)]
  }
  
  Headers.prototype.get = function(name) {
    name = normalizeName(name)
    return this.has(name) ? this.map[name] : null
  }
  
  Headers.prototype.has = function(name) {
    return this.map.hasOwnProperty(normalizeName(name))
  }
  
  Headers.prototype.set = function(name, value) {
    this.map[normalizeName(name)] = normalizeValue(value)
  }
  
  Headers.prototype.forEach = function(callback, thisArg) {
    for (var name in this.map) {
      if (this.map.hasOwnProperty(name)) {
        callback.call(thisArg, this.map[name], name, this)
      }
    }
  }
  
  Headers.prototype.keys = function() {
    var items = []
    this.forEach(function(value, name) {
      items.push(name)
    })
    return iteratorFor(items)
  }
  
  Headers.prototype.values = function() {
    var items = []
    this.forEach(function(value) {
      items.push(value)
    })
    return iteratorFor(items)
  }
  
  Headers.prototype.entries = function() {
    var items = []
    this.forEach(function(value, name) {
      items.push([name, value])
    })
    return iteratorFor(items)
  }
  
  if (support.iterable) {
    Headers.prototype[Symbol.iterator] = Headers.prototype.entries
  }
  
  function consumed(body) {
    if (body.bodyUsed) {
      return Promise.reject(new TypeError('Already read'))
    }
    body.bodyUsed = true
  }
  
  function fileReaderReady(reader) {
    return new Promise(function(resolve, reject) {
      reader.onload = function() {
        resolve(reader.result)
      }
      reader.onerror = function() {
        reject(reader.error)
      }
    })
  }
  
  function readBlobAsArrayBuffer(blob) {
    var reader = new FileReader()
    var promise = fileReaderReady(reader)
    reader.readAsArrayBuffer(blob)
    return promise
  }
  
  function readBlobAsText(blob) {
    var reader = new FileReader()
    var promise = fileReaderReady(reader)
    reader.readAsText(blob)
    return promise
  }
  
  function readArrayBufferAsText(buf) {
    var view = new Uint8Array(buf)
    var chars = new Array(view.length)
  
    for (var i = 0; i < view.length; i++) {
      chars[i] = String.fromCharCode(view[i])
    }
    return chars.join('')
  }
  
  function bufferClone(buf) {
    if (buf.slice) {
      return buf.slice(0)
    } else {
      var view = new Uint8Array(buf.byteLength)
      view.set(new Uint8Array(buf))
      return view.buffer
    }
  }
  
  function Body() {
    this.bodyUsed = false
  
    this._initBody = function(body) {
      /*
        fetch-mock wraps the Response object in an ES6 Proxy to
        provide useful test harness features such as flush. However, on
        ES5 browsers without fetch or Proxy support pollyfills must be used;
        the proxy-pollyfill is unable to proxy an attribute unless it exists
        on the object before the Proxy is created. This change ensures
        Response.bodyUsed exists on the instance, while maintaining the
        semantic of setting Request.bodyUsed in the constructor before
        _initBody is called.
      */
      this.bodyUsed = this.bodyUsed
      this._bodyInit = body
      if (!body) {
        this._bodyText = ''
      } else if (typeof body === 'string') {
        this._bodyText = body
      } else if (support.blob && Blob.prototype.isPrototypeOf(body)) {
        this._bodyBlob = body
      } else if (support.formData && FormData.prototype.isPrototypeOf(body)) {
        this._bodyFormData = body
      } else if (support.searchParams && URLSearchParams.prototype.isPrototypeOf(body)) {
        this._bodyText = body.toString()
      } else if (support.arrayBuffer && support.blob && isDataView(body)) {
        this._bodyArrayBuffer = bufferClone(body.buffer)
        // IE 10-11 can't handle a DataView body.
        this._bodyInit = new Blob([this._bodyArrayBuffer])
      } else if (support.arrayBuffer && (ArrayBuffer.prototype.isPrototypeOf(body) || isArrayBufferView(body))) {
        this._bodyArrayBuffer = bufferClone(body)
      } else {
        this._bodyText = body = Object.prototype.toString.call(body)
      }
  
      if (!this.headers.get('content-type')) {
        if (typeof body === 'string') {
          this.headers.set('content-type', 'text/plain;charset=UTF-8')
        } else if (this._bodyBlob && this._bodyBlob.type) {
          this.headers.set('content-type', this._bodyBlob.type)
        } else if (support.searchParams && URLSearchParams.prototype.isPrototypeOf(body)) {
          this.headers.set('content-type', 'application/x-www-form-urlencoded;charset=UTF-8')
        }
      }
    }
  
    if (support.blob) {
      this.blob = function() {
        var rejected = consumed(this)
        if (rejected) {
          return rejected
        }
  
        if (this._bodyBlob) {
          return Promise.resolve(this._bodyBlob)
        } else if (this._bodyArrayBuffer) {
          return Promise.resolve(new Blob([this._bodyArrayBuffer]))
        } else if (this._bodyFormData) {
          throw new Error('could not read FormData body as blob')
        } else {
          return Promise.resolve(new Blob([this._bodyText]))
        }
      }
  
      this.arrayBuffer = function() {
        if (this._bodyArrayBuffer) {
          return consumed(this) || Promise.resolve(this._bodyArrayBuffer)
        } else {
          return this.blob().then(readBlobAsArrayBuffer)
        }
      }
    }
  
    this.text = function() {
      var rejected = consumed(this)
      if (rejected) {
        return rejected
      }
  
      if (this._bodyBlob) {
        return readBlobAsText(this._bodyBlob)
      } else if (this._bodyArrayBuffer) {
        return Promise.resolve(readArrayBufferAsText(this._bodyArrayBuffer))
      } else if (this._bodyFormData) {
        throw new Error('could not read FormData body as text')
      } else {
        return Promise.resolve(this._bodyText)
      }
    }
  
    if (support.formData) {
      this.formData = function() {
        return this.text().then(decode)
      }
    }
  
    this.json = function() {
      return this.text().then(JSON.parse)
    }
  
    return this
  }
  
  // HTTP methods whose capitalization should be normalized
  var methods = ['DELETE', 'GET', 'HEAD', 'OPTIONS', 'POST', 'PUT']
  
  function normalizeMethod(method) {
    var upcased = method.toUpperCase()
    return methods.indexOf(upcased) > -1 ? upcased : method
  }
  
  export function Request(input, options) {
    options = options || {}
    var body = options.body
  
    if (input instanceof Request) {
      if (input.bodyUsed) {
        throw new TypeError('Already read')
      }
      this.url = input.url
      this.credentials = input.credentials
      if (!options.headers) {
        this.headers = new Headers(input.headers)
      }
      this.method = input.method
      this.mode = input.mode
      this.signal = input.signal
      if (!body && input._bodyInit != null) {
        body = input._bodyInit
        input.bodyUsed = true
      }
    } else {
      this.url = String(input)
    }
  
    this.credentials = options.credentials || this.credentials || 'same-origin'
    if (options.headers || !this.headers) {
      this.headers = new Headers(options.headers)
    }
    this.method = normalizeMethod(options.method || this.method || 'GET')
    this.mode = options.mode || this.mode || null
    this.signal = options.signal || this.signal
    this.referrer = null
  
    if ((this.method === 'GET' || this.method === 'HEAD') && body) {
      throw new TypeError('Body not allowed for GET or HEAD requests')
    }
    this._initBody(body)
  }
  
  Request.prototype.clone = function() {
    return new Request(this, {body: this._bodyInit})
  }
  
  function decode(body) {
    var form = new FormData()
    body
      .trim()
      .split('&')
      .forEach(function(bytes) {
        if (bytes) {
          var split = bytes.split('=')
          var name = split.shift().replace(/\+/g, ' ')
          var value = split.join('=').replace(/\+/g, ' ')
          form.append(decodeURIComponent(name), decodeURIComponent(value))
        }
      })
    return form
  }
  
  function parseHeaders(rawHeaders) {
    var headers = new Headers()
    // Replace instances of \r\n and \n followed by at least one space or horizontal tab with a space
    // https://tools.ietf.org/html/rfc7230#section-3.2
    var preProcessedHeaders = rawHeaders.replace(/\r?\n[\t ]+/g, ' ')
    preProcessedHeaders.split(/\r?\n/).forEach(function(line) {
      var parts = line.split(':')
      var key = parts.shift().trim()
      if (key) {
        var value = parts.join(':').trim()
        headers.append(key, value)
      }
    })
    return headers
  }
  
  Body.call(Request.prototype)
  
  export function Response(bodyInit, options) {
    if (!options) {
      options = {}
    }
  
    this.type = 'default'
    this.status = options.status === undefined ? 200 : options.status
    this.ok = this.status >= 200 && this.status < 300
    this.statusText = 'statusText' in options ? options.statusText : ''
    this.headers = new Headers(options.headers)
    this.url = options.url || ''
    this._initBody(bodyInit)
  }
  
  Body.call(Response.prototype)
  
  Response.prototype.clone = function() {
    return new Response(this._bodyInit, {
      status: this.status,
      statusText: this.statusText,
      headers: new Headers(this.headers),
      url: this.url
    })
  }
  
  Response.error = function() {
    var response = new Response(null, {status: 0, statusText: ''})
    response.type = 'error'
    return response
  }
  
  var redirectStatuses = [301, 302, 303, 307, 308]
  
  Response.redirect = function(url, status) {
    if (redirectStatuses.indexOf(status) === -1) {
      throw new RangeError('Invalid status code')
    }
  
    return new Response(null, {status: status, headers: {location: url}})
  }
  
  export var DOMException = self.DOMException
  try {
    new DOMException()
  } catch (err) {
    DOMException = function(message, name) {
      this.message = message
      this.name = name
      var error = Error(message)
      this.stack = error.stack
    }
    DOMException.prototype = Object.create(Error.prototype)
    DOMException.prototype.constructor = DOMException
  }
  
  export function fetch(input, init) {
    return new Promise(function(resolve, reject) {
      var request = new Request(input, init)
  
      if (request.signal && request.signal.aborted) {
        return reject(new DOMException('Aborted', 'AbortError'))
      }
  
      var xhr = new XMLHttpRequest()
  
      function abortXhr() {
        xhr.abort()
      }
  
      xhr.onload = function() {
        var options = {
          status: xhr.status,
          statusText: xhr.statusText,
          headers: parseHeaders(xhr.getAllResponseHeaders() || '')
        }
        options.url = 'responseURL' in xhr ? xhr.responseURL : options.headers.get('X-Request-URL')
        var body = 'response' in xhr ? xhr.response : xhr.responseText
        setTimeout(function() {
          resolve(new Response(body, options))
        }, 0)
      }
  
      xhr.onerror = function() {
        setTimeout(function() {
          reject(new TypeError('Network request failed'))
        }, 0)
      }
  
      xhr.ontimeout = function() {
        setTimeout(function() {
          reject(new TypeError('Network request failed'))
        }, 0)
      }
  
      xhr.onabort = function() {
        setTimeout(function() {
          reject(new DOMException('Aborted', 'AbortError'))
        }, 0)
      }
  
      function fixUrl(url) {
        try {
          return url === '' && self.location.href ? self.location.href : url
        } catch (e) {
          return url
        }
      }
  
      xhr.open(request.method, fixUrl(request.url), true)
  
      if (request.credentials === 'include') {
        xhr.withCredentials = true
      } else if (request.credentials === 'omit') {
        xhr.withCredentials = false
      }
  
      if ('responseType' in xhr) {
        if (support.blob) {
          xhr.responseType = 'blob'
        } else if (
          support.arrayBuffer &&
          request.headers.get('Content-Type').indexOf('application/octet-stream') !== -1
        ) {
          xhr.responseType = 'arraybuffer'
        }
      }
  
      request.headers.forEach(function(value, name) {
        xhr.setRequestHeader(name, value)
      })
  
      if (request.signal) {
        request.signal.addEventListener('abort', abortXhr)
  
        xhr.onreadystatechange = function() {
          // DONE (success or failure)
          if (xhr.readyState === 4) {
            request.signal.removeEventListener('abort', abortXhr)
          }
        }
      }
  
      xhr.send(typeof request._bodyInit === 'undefined' ? null : request._bodyInit)
    })
  }
  
  fetch.polyfill = true
  
  // 先备份
  var originHeaders = self.Headers;
  var originRequest = self.Request;
  var originResponse = self.Response;
  var originFetch = self.fetch;
  
  if (!self.fetch) {
    self.fetch = fetch
    self.Headers = Headers
    self.Request = Request
    self.Response = Response
  }
  
  export function enableFetchHook(enable) {
    if (originFetch) { // 如果当前系统支持 fetch，才需要 hook
      if (enable) {
        // 开启 fetch hook
        self.fetch = fetch;
        self.Headers = Headers;
        self.Request = Request;
        self.Response = Response;
      } else {
        // 关闭 fetch hook
        self.fetch = originFetch;
        self.Headers = originHeaders;
        self.Request = originRequest;
        self.Response = originResponse;
      }
    }
  };
  