XMLHttpRequest polyfill issue

[wkh237]

Derived #69

[wkh237]

@kdedakia, after the investigation, I've located a problem in our XMLHttpRequest implementation, when response header contains Content-Type : application/json, the xhr.response propertywill be converted to object (which simply JSON.parse xhr.responseText), this is based on my understanding to W3C standard.

However, the WHATWG-Fetch implementation and those ones in many browsers seems not convert xhr.response to JSON object when response header has the application/json content type, and this is why fetch does not working after replacing the XMLHttpRequest. The following code snippet is the body parser of WHATWG-Fetch

function Body() {
    this.bodyUsed = false

    this._initBody = function(body) {
      this._bodyInit = body
      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 (!body) {
        this._bodyText = ''
      } else if (support.arrayBuffer && ArrayBuffer.prototype.isPrototypeOf(body)) {
        // Only support ArrayBuffers for POST method.
        // Receiving ArrayBuffers happens via Blobs, instead.
      } else {
        throw new Error('unsupported BodyInit type')
      }

Since it does not ever expect xhr.response would be an object, it always throws error. I've change our implementation to fit the spec. You can try install the beta version and see if that works properly.

$ rnpm install --save react-native-fetch-blob@beta

However, when the response is binary data it may not working properly, in this case, you can use our network APIs as an alternative 😏

[mlumbroso]

Working great for me now !