Summary:
So far, XHR only supports a few `onfoo` event handlers, not the entier `EventTarget` interface (`addEventListener`, `removeEventListener`). It also doesn't support the `upload` object on Android -- for no good reason. Even if we don't send any events there yet, there's no reason we have to break consuming code that wants to register an event handler there. This PR rectifies all that.
Fortunately, adding proper `EventTarget` support is very easy thanks to `event-target-shim`. We already use it in our WebSocket implementation. It transparently handles the `addEventListener('foo', ...)` as well as `onfoo` APIs, so when you dispatch an event on the event target, the right handlers will be invoked. The event object is wrapped so that `event.target` is set properly. Basically, it's a super easy way to make us conform to the spec.
Also added a bit of polish here and there, using ES2015 class property goodness to consolidate a lot of Flow property definitions with the corresponding property initializers.
**T
Closes https://github.com/facebook/react-native/pull/7017
Reviewed By: fkgozali
Differential Revision: D3202021
Pulled By: martinbigio
fb-gh-sync-id: 2b007682074356c75c774fab337672918b6c4355
fbshipit-source-id: 2b007682074356c75c774fab337672918b6c4355
Summary:Currently React-Native does not have `ontimeout` and `onerror` handlers for [XMLHttpRequest](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest). This is an extension to [No timeout on XMLHttpRequest](https://github.com/facebook/react-native/issues/4648).
With addition to two handlers, both Android and iOS can now handle `ontimeout` if request times out and `onerror` when there is general network error.
**Test plan**
Code has been tested on both Android and iOS with [Charles](https://www.charlesproxy.com/) by setting a breakpoint on the request which fires `ontimeout` when the request waits beyond `timeout` time and `onerror` when there is network error.
**Usage**
JavaScript -
```
var request = new XMLHttpRequest();
function onLoad() {
console.log(request.status);
};
function onTimeout() {
console.log('Timeout');
};
function onError() {
console.log('General network error');
};
request.onload = onLoad;
request.ontimeout = onTimeout;
request.onerr
Closes https://github.com/facebook/react-native/pull/6841
Differential Revision: D3178859
Pulled By: lexs
fb-gh-sync-id: 30674570653e92ab5f7e74bd925dd5640fc862b6
fbshipit-source-id: 30674570653e92ab5f7e74bd925dd5640fc862b6
Philipp von Weitershausen
Christoph Pojer
grgmo