Track XHR replacements correctly (#2455)

* Track XHR replacements correctly

Fixes #2439

* Update docs [skip ci]

docs/change-log.md

@@ -115,6 +115,7 @@
 - render: correct `contenteditable` check to also check for `contentEditable` property name ([#2450](https://github.com/MithrilJS/mithril.js/pull/2450) [@isiahmeadows](https://github.com/isiahmeadows))
 - docs: clarify valid key usage ([#2452](https://github.com/MithrilJS/mithril.js/pull/2452) [@isiahmeadows](https://github.com/isiahmeadows))
 - route: don't pollute globals ([#2453](https://github.com/MithrilJS/mithril.js/pull/2453) [@isiahmeadows](https://github.com/isiahmeadows))
+- request: track xhr replacements correctly ([#2455](https://github.com/MithrilJS/mithril.js/pull/2455) [@isiahmeadows](https://github.com/isiahmeadows))
 
 ---
 

docs/index.md

@@ -18,7 +18,7 @@ It's small (< 10kb gzip), fast and provides routing and XHR utilities out of the
 <div style="display:flex;margin:0 0 30px;">
 	<div style="width:50%;">
 		<h5>Download size</h5>
-		<small>Mithril (9.5kb)</small>
+		<small>Mithril (9.6kb)</small>
 		<div style="animation:grow 0.08s;background:#1e5799;height:3px;margin:0 10px 10px 0;transform-origin:0;width:4%;"></div>
 		<small style="color:#aaa;">Vue + Vue-Router + Vuex + fetch (40kb)</small>
 		<div style="animation:grow 0.4s;background:#1e5799;height:3px;margin:0 10px 10px 0;transform-origin:0;width:20%"></div>

docs/request.md

@@ -54,7 +54,7 @@ Argument                  | Type                              | Required | Descr
 `options.withCredentials` | `Boolean`                         | No       | Whether to send cookies to 3rd party domains. Defaults to `false`
 `options.timeout`         | `Number`                          | No       | The amount of milliseconds a request can take before automatically being [terminated](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/timeout).  Defaults to `undefined`.
 `options.responseType`    | `String`                          | No       | The expected [type](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/responseType) of the response. Defaults to `""` if `extract` is defined, `"json"` if missing. If `responseType: "json"`, it internally performs `JSON.parse(responseText)`.
-`options.config`          | `xhr = Function(xhr)`             | No       | Exposes the underlying XMLHttpRequest object for low-level configuration. Defaults to the [identity function](https://en.wikipedia.org/wiki/Identity_function).
+`options.config`          | `xhr = Function(xhr)`             | No       | Exposes the underlying XMLHttpRequest object for low-level configuration and optional replacement (by returning a new XHR).
 `options.headers`         | `Object`                          | No       | Headers to append to the request before sending it (applied right before `options.config`).
 `options.type`            | `any = Function(any)`             | No       | A constructor to be applied to each object in the response. Defaults to the [identity function](https://en.wikipedia.org/wiki/Identity_function).
 `options.serialize`       | `string = Function(any)`          | No       | A serialization method to be applied to `body`. Defaults to `JSON.stringify`, or if `options.body` is an instance of [`FormData`](https://developer.mozilla.org/en/docs/Web/API/FormData), defaults to the [identity function](https://en.wikipedia.org/wiki/Identity_function) (i.e. `function(value) {return value}`).