js: Add option to configure the fetch method

Author: svix-mman

codegen/templates/javascript/summary.ts.jinja

@@ -27,6 +27,11 @@ export type SvixOptions = {
   serverUrl?: string;
   /** Time in milliseconds to wait for requests to get a response. */
   requestTimeout?: number;
+  /**
+   * Custom fetch implementation to use for HTTP requests.
+   * Useful for testing, adding custom middleware, or running in non-standard environments.
+   */
+  fetch?: typeof fetch;
 } & XOR<
   {
     /** List of delays (in milliseconds) to wait before each retry attempt.*/
@@ -63,6 +68,7 @@ export class Svix {
         token,
         timeout: options.requestTimeout,
         retryScheduleInMs: options.retryScheduleInMs,
+        fetch: options.fetch,
       };
       return;
     }
@@ -72,13 +78,15 @@ export class Svix {
         token,
         timeout: options.requestTimeout,
         numRetries: options.numRetries,
+        fetch: options.fetch,
       };
       return;
     }
     this.requestCtx = {
       baseUrl,
       token,
       timeout: options.requestTimeout,
+      fetch: options.fetch,
     };
   }
 

javascript/src/index.ts

@@ -36,6 +36,11 @@ export type SvixOptions = {
   serverUrl?: string;
   /** Time in milliseconds to wait for requests to get a response. */
   requestTimeout?: number;
+  /**
+   * Custom fetch implementation to use for HTTP requests.
+   * Useful for testing, adding custom middleware, or running in non-standard environments.
+   */
+  fetch?: typeof fetch;
 } & XOR<
   {
     /** List of delays (in milliseconds) to wait before each retry attempt.*/
@@ -71,6 +76,7 @@ export class Svix {
         token,
         timeout: options.requestTimeout,
         retryScheduleInMs: options.retryScheduleInMs,
+        fetch: options.fetch,
       };
       return;
     }
@@ -80,13 +86,15 @@ export class Svix {
         token,
         timeout: options.requestTimeout,
         numRetries: options.numRetries,
+        fetch: options.fetch,
       };
       return;
     }
     this.requestCtx = {
       baseUrl,
       token,
       timeout: options.requestTimeout,
+      fetch: options.fetch,
     };
   }
 

javascript/src/mockttp.test.ts

@@ -500,4 +500,22 @@ test("mockttp tests", async (t) => {
     const requests = await endpointMock.getSeenRequests();
     assert.equal(requests.length, 1);
   });
+
+  await t.test("should use custom fetch implementation", async () => {
+    let customFetchCalled = false;
+    const mockFetch: typeof fetch = async (_input, _init) => {
+      customFetchCalled = true;
+      return new Response(ListResponseApplicationOut, {
+        status: 200,
+        headers: { "Content-Type": "application/json" },
+      });
+    };
+
+    await mockServer
+      .forGet(/\/api\/v1\/app.*/)
+      .thenReply(200, ListResponseApplicationOut);
+    const svx = new Svix("token", { serverUrl: mockServer.url, fetch: mockFetch });
+    await svx.application.list({ order: Ordering.Ascending });
+    assert(customFetchCalled);
+  });
 });

javascript/src/request.ts

@@ -24,6 +24,11 @@ export type SvixRequestContext = {
   token: string;
   /** Time in milliseconds to wait for requests to get a response. */
   timeout?: number;
+  /**
+   * Custom fetch implementation to use for HTTP requests.
+   * Useful for testing, adding custom middleware, or running in non-standard environments.
+   */
+  fetch?: typeof fetch;
 } & XOR<
   {
     /** List of delays (in milliseconds) to wait before each retry attempt.*/
@@ -159,7 +164,8 @@ export class SvixRequest {
       },
       ctx.retryScheduleInMs,
       ctx.retryScheduleInMs?.[0],
-      ctx.retryScheduleInMs?.length || ctx.numRetries
+      ctx.retryScheduleInMs?.length || ctx.numRetries,
+      ctx.fetch
     );
     return filterResponseForErrors(response);
   }
@@ -200,13 +206,14 @@ async function sendWithRetry(
   retryScheduleInMs?: number[],
   nextInterval = 50,
   triesLeft = 2,
+  fetchImpl: typeof fetch = fetch,
   retryCount = 1
 ): Promise<Response> {
   const sleep = (interval: number) =>
     new Promise((resolve) => setTimeout(resolve, interval));
 
   try {
-    const response = await fetch(url, init);
+    const response = await fetchImpl(url, init);
     if (triesLeft <= 0 || response.status < 500) {
       return response;
     }
@@ -225,6 +232,7 @@ async function sendWithRetry(
     retryScheduleInMs,
     nextInterval,
     --triesLeft,
+    fetchImpl,
     ++retryCount
   );
 }