[feature] Enable customizing networking library reducing bundle size

docs/guides/custom-networking.md

@@ -4,45 +4,66 @@ sidebar_label: Custom networking library
 ---
 The default `fetch()` implementation uses [superagent]() due to it's server-side support
 and excellent builder-pattern api. However, a simple overriding of the `fetch()` function
-will enable you to use any networking library you please.
+will enable you to use any networking library you please. By extending from `SimpleResource`
+instead of `Resource` you can potentially reduce your bundle size by enabling the superagent
+library to be tree-shaken away.
 
 ### Default fetch with superagent:
 
 ```typescript
+import request from 'superagent';
+import { Method } from '~/types';
+
+import SimpleResource from './SimpleResource';
+
+/** Represents an entity to be retrieved from a server. Typically 1:1 with a url endpoint. */
+export default abstract class Resource extends SimpleResource {
+  /** A function to mutate all requests for fetch */
+  static fetchPlugin?: request.Plugin;
+
   /** Perform network request and resolve with json body */
-  static async fetch<T extends typeof Resource>(
+  static fetch<T extends typeof Resource>(
     this: T,
-    method: Method = 'get',
+    method: Method,
     url: string,
     body?: Readonly<object>,
   ) {
     let req = request[method](url).on('error', () => {});
     if (this.fetchPlugin) req = req.use(this.fetchPlugin);
     if (body) req = req.send(body);
-    const json = (await req).body;
-    return json;
+    return req.then(res => {
+      if (process.env.NODE_ENV !== 'production') {
+        if (!res.type.includes('json') && Object.keys(res.body).length === 0) {
+          throw new Error('JSON expected but not returned from API');
+        }
+      }
+      return res.body;
+    });
   }
+}
 ```
 
 Here are examples using other popular networking APIs:
 
-## [Fetch](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API)
+## Fetch
+
+[Fetch](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API)
 
 ```typescript
-import { Resource, Method } from 'rest-hooks';
+import { SimpleResource, Method } from 'rest-hooks';
 
-export default abstract class FetchResource extends Resource {
+export default abstract class FetchResource extends SimpleResource {
   /** A function to mutate all request options for fetch */
   static fetchOptionsPlugin?: (options: RequestInit) => RequestInit;
 
   /** Perform network request and resolve with json body */
-  static async fetch<T extends typeof Resource>(
+  static async fetch<T extends typeof SimpleResource>(
     this: T,
-    method: Method = 'get',
+    method: Method,
     url: string,
     body?: Readonly<object>
   ) {
-    let options = {
+    let options: RequestInit = {
       method: method.toUpperCase(),
       credentials: 'same-origin',
       headers: {
@@ -59,17 +80,19 @@ export default abstract class FetchResource extends Resource {
 }
 ```
 
-## [Axios](https://github.com/axios/axios)
+## Axios
+
+[Axios](https://github.com/axios/axios)
 
 ```typescript
-import { Resource, Method } from 'rest-hooks';
+import { SimpleResource, Method } from 'rest-hooks';
 import axios from 'axios';
 
-export default abstract class AxiosResource extends Resource {
+export default abstract class AxiosResource extends SimpleResource {
   /** Perform network request and resolve with json body */
-  static async fetch<T extends typeof Resource>(
+  static async fetch<T extends typeof AxiosResource>(
     this: T,
-    method: Method = 'get',
+    method: Method,
     url: string,
     body?: Readonly<object>
   ) {