feat: Add the ability to pass custom fetch functions

README.md

@@ -4,7 +4,7 @@
 [![codecov badge](https://codecov.io/gh/haverstack/axios-fetch-adapter/branch/main/graph/badge.svg?token=J2J0ANDB3F)](https://codecov.io/gh/haverstack/axios-fetch-adapter)
 [![license badge](https://img.shields.io/github/license/haverstack/axios-fetch-adapter)](./LICENSE)
 
-An Axios adapter that uses native `fetch`. Useful for Cloudflare Workers and ServiceWorker environments.
+An Axios adapter that uses native `fetch` or a custom `fetch` function. Useful for Cloudflare Workers and ServiceWorker environments.
 
 > **Note:** This adapter was designed for version `0.21.1` of Axios, which is still used in prominent e-commerce SDKs.
 
@@ -23,6 +23,18 @@ const client = axios.create({
 });
 ```
 
+To use with a custom `fetch` function:
+```javascript
+import axios from "axios";
+import { createFetchAdapter } from "@haverstack/axios-fetch-adapter";
+import myCustomFetch from "my-custom-fetch";
+
+const myCustomFetchAdapter = createFetchAdapter({ fetch: myCustomFetch });
+const client = axios.create({
+  adapter: myCustomFetchAdapter
+});
+```
+
 To use with the Square API:
 ```javascript
 import { Client, Environment } from "square";

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@haverstack/axios-fetch-adapter",
-  "version": "0.7.0",
-  "description": "An Axios adapter that uses native fetch. Useful for Cloudflare Workers and ServiceWorker environments.",
+  "version": "0.8.0",
+  "description": "An Axios adapter that uses native fetch or custom fetch functions. Useful for Cloudflare Workers and ServiceWorker environments.",
   "main": "lib/index.js",
   "types": "lib/index.d.ts",
   "module": "lib/index.esm.js",

src/index.test.ts

@@ -1,5 +1,6 @@
-import fetchAdapter from ".";
+import fetchAdapter, { createFetchAdapter } from ".";
 import type { AxiosError } from "axios";
+import axios from "axios";
 
 // Test URL
 const url = "http://localhost:1";
@@ -153,6 +154,16 @@ test("Serialization set with `paramsSerializer` produces correct results", async
   expect(result.request.url).toBe(`${url}/?foo=100`);
 });
 
+test("Can set custom `fetch` functions", async () => {
+  const testMsg = "Custom fetch!";
+  const myFetch = async (_: RequestInfo | URL) => {
+    return new Response(testMsg);
+  };
+  const axiosInstance = axios.create({ adapter: createFetchAdapter({ fetch: myFetch }) });
+  const result = await axiosInstance.get(url);
+  expect(result.data).toBe(testMsg);
+});
+
 test("Invalid request will throw an error", async () => {
   // Disables fetch mock for the rest of this file
   jest.restoreAllMocks();

src/index.ts

@@ -31,58 +31,75 @@ import { AxiosError, AxiosRequestConfig, AxiosResponse } from "axios";
 import buildURL from "axios/lib/helpers/buildURL";
 import { buildFullPath } from "./buildFullPath";
 
-export default async function fetchAdapter(config: AxiosRequestConfig): Promise<AxiosResponse> {
-  const request = createRequest(config);
-  const promiseChain = [getResponse(request, config)];
-  let timer: NodeJS.Timeout | null = null;
-
-  if (config.timeout && config.timeout > 0) {
-    promiseChain.push(
-      new Promise((_, reject) => {
-        timer = setTimeout(() => {
-          const message = config.timeoutErrorMessage
-            ? config.timeoutErrorMessage
-            : "timeout of " + config.timeout + "ms exceeded";
-          reject(createError(message, config, "ETIMEDOUT", request));
-        }, config.timeout);
-      })
-    );
-  }
+type FetchFunction = (
+  input: RequestInfo | URL,
+  init?: RequestInit | undefined
+) => Promise<Response>;
+type AdapterFunction = (config: AxiosRequestConfig) => Promise<AxiosResponse>;
+interface FetchAdapterConfig {
+  fetch: FetchFunction;
+}
 
-  const response = await Promise.race(promiseChain);
-  // Cancel the timeout timer if it's set
-  if (timer !== null) {
-    clearTimeout(timer);
-  }
-  return new Promise((resolve, reject) => {
-    if (response instanceof Error) {
-      reject(response);
-    } else {
-      const validateStatus = config.validateStatus;
-      if (!response.status || !validateStatus || validateStatus(response.status)) {
-        resolve(response);
+export function createFetchAdapter(fetchConfig?: FetchAdapterConfig): AdapterFunction {
+  const adapterFetch = fetchConfig ? fetchConfig.fetch : undefined;
+  async function axiosAdapter(config: AxiosRequestConfig): Promise<AxiosResponse> {
+    const request = createRequest(config);
+    const promiseChain = [getResponse(request, config, adapterFetch)];
+    let timer: NodeJS.Timeout | null = null;
+
+    if (config.timeout && config.timeout > 0) {
+      promiseChain.push(
+        new Promise((_, reject) => {
+          timer = setTimeout(() => {
+            const message = config.timeoutErrorMessage
+              ? config.timeoutErrorMessage
+              : "timeout of " + config.timeout + "ms exceeded";
+            reject(createError(message, config, "ETIMEDOUT", request));
+          }, config.timeout);
+        })
+      );
+    }
+
+    const response = await Promise.race(promiseChain);
+    // Cancel the timeout timer if it's set
+    if (timer !== null) {
+      clearTimeout(timer);
+    }
+    return new Promise((resolve, reject) => {
+      if (response instanceof Error) {
+        reject(response);
       } else {
-        reject(
-          createError(
-            "Request failed with status code " + response.status,
-            config,
-            getErrorCodeFromStatus(response.status),
-            request,
-            response
-          )
-        );
+        const validateStatus = config.validateStatus;
+        if (!response.status || !validateStatus || validateStatus(response.status)) {
+          resolve(response);
+        } else {
+          reject(
+            createError(
+              "Request failed with status code " + response.status,
+              config,
+              getErrorCodeFromStatus(response.status),
+              request,
+              response
+            )
+          );
+        }
       }
-    }
-  });
+    });
+  }
+  return axiosAdapter;
 }
 
+const fetchAdapter = createFetchAdapter();
+export default fetchAdapter;
+
 async function getResponse(
   request: Request,
-  config: AxiosRequestConfig
+  config: AxiosRequestConfig,
+  adapterFetch: FetchFunction = fetch
 ): Promise<(AxiosResponse & { ok: boolean }) | AxiosError> {
   let stageOne;
   try {
-    stageOne = await fetch(request);
+    stageOne = await adapterFetch(request);
   } catch (e) {
     return createError("Network Error", config, "ERR_NETWORK", request);
   }