fix: support edge/serverless runtimes via axios adapter fallback (#31)

README.md

@@ -44,6 +44,14 @@ const mailerlite = new MailerLite({
 });
 ```
 
+### Edge & serverless runtimes
+
+The SDK works in edge/serverless runtimes that don't ship Node's `http`
+module — such as Vercel Edge Functions, Cloudflare Workers, Next.js edge
+routes and Deno. Requests automatically fall back to the `fetch` adapter
+in those environments, while Node and browsers keep using their existing
+adapters unchanged.
+
 - [Subscribers](src/modules/subscribers/README.md)
     * [List all subscribers](src/modules/subscribers/README.md#list-all-subscribers)
     * [Create/update subscriber](src/modules/subscribers/README.md#createupdate-subscriber)

src/utils/fetch.test.ts

@@ -0,0 +1,30 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// `vi.mock` is hoisted to the top of the file, so the mock fn has to be
+// created with `vi.hoisted` to be available inside the factory.
+const axiosMock = vi.hoisted(() => vi.fn(() => Promise.resolve({ data: {} })));
+vi.mock("axios", () => ({ default: axiosMock }));
+
+import request from "./fetch";
+import { Config } from "./types";
+
+const config: Config = {
+    api_key: "test-key",
+    basePath: "https://connect.mailerlite.com",
+};
+
+describe("request adapter selection", () => {
+    beforeEach(() => {
+        axiosMock.mockClear();
+    });
+
+    it("asks axios to fall back through http -> xhr -> fetch", async () => {
+        await request("/api/subscribers", { method: "GET" }, config);
+
+        expect(axiosMock).toHaveBeenCalledTimes(1);
+        const passedConfig = axiosMock.mock.calls[0][0] as { adapter: unknown };
+        // Ordering matters: Node/browser keep their existing adapter, while
+        // edge/serverless runtimes fall back to `fetch`. See issue #31.
+        expect(passedConfig.adapter).toEqual(["http", "xhr", "fetch"]);
+    });
+});

src/utils/fetch.ts

@@ -25,7 +25,12 @@ export default function request(endpoint: string = "", options: Options, config:
             "Content-type": "application/json",
             "accept-encoding": "null" // needed for axios
         },
-        data: body && JSON.stringify(body)
+        data: body && JSON.stringify(body),
+        // Let axios pick the first adapter supported by the current runtime.
+        // Node keeps using `http` and browsers keep using `xhr` (no behaviour
+        // change), while edge/serverless runtimes (Vercel Edge, Cloudflare
+        // Workers, Deno, Next.js edge) that ship neither fall back to `fetch`.
+        adapter: ["http", "xhr", "fetch"]
     })
 }