refactor(ajax): Use simple Observable

- Refactors `ajax` to use a simple `Observable` implementation.
- Moves code to a new ajax-specific folder.
- Adds a lot more documentation to classes and support classes.
- Differentiates between the configuration passed to `ajax` (`AjaxConfig`) and the request values used to make the HTTP request (`AjaxRequest`), as the latter has more required values.
- Ensures that no configuration values are mutated while making the request.
- Ensures there is at least one valid test for `ajax.patch`. The old one was sketchy.
- Adds better comments throughout the code.
- Adds better typing to `ajax` functions.

BREAKING CHANGE: For TypeScript users, `AjaxRequest` is no longer the type that should be explicitly used to create an `ajax`. It is now `AjaxConfig`, although the two types are compatible, only `AjaxConfig` has `progressSubscriber` and `createXHR`.

api_guard/dist/types/ajax/index.d.ts

@@ -1,40 +1,52 @@
 export declare const ajax: AjaxCreationMethod;
 
-export interface AjaxError extends Error {
-    request: AjaxRequest;
-    response: any;
-    responseType: XMLHttpRequestResponseType;
-    status: number;
-    xhr: XMLHttpRequest;
-}
-
-export declare const AjaxError: AjaxErrorCtor;
-
-export interface AjaxRequest {
+export interface AjaxConfig {
     async?: boolean;
     body?: any;
     createXHR?: () => XMLHttpRequest;
     crossDomain?: boolean;
-    hasContent?: boolean;
-    headers?: object;
+    headers?: Readonly<Record<string, any>>;
     method?: string;
     password?: string;
     progressSubscriber?: PartialObserver<ProgressEvent>;
-    responseType?: string;
+    responseType?: XMLHttpRequestResponseType;
     timeout?: number;
-    url?: string;
+    url: string;
     user?: string;
     withCredentials?: boolean;
 }
 
-export declare class AjaxResponse {
-    originalEvent: Event;
+export interface AjaxError extends Error {
     request: AjaxRequest;
     response: any;
-    responseText: string;
-    responseType: string;
+    responseType: XMLHttpRequestResponseType;
     status: number;
     xhr: XMLHttpRequest;
+}
+
+export declare const AjaxError: AjaxErrorCtor;
+
+export interface AjaxRequest {
+    async: boolean;
+    body?: any;
+    crossDomain: boolean;
+    headers: Readonly<Record<string, any>>;
+    method: string;
+    password?: string;
+    responseType: XMLHttpRequestResponseType;
+    timeout: number;
+    url: string;
+    user?: string;
+    withCredentials: boolean;
+}
+
+export declare class AjaxResponse<T> {
+    readonly originalEvent: Event;
+    readonly request: AjaxRequest;
+    readonly response: T;
+    readonly responseType: XMLHttpRequestResponseType;
+    readonly status: number;
+    readonly xhr: XMLHttpRequest;
     constructor(originalEvent: Event, xhr: XMLHttpRequest, request: AjaxRequest);
 }