fix: do not proxy then. fixes #107 (#108)

Author: Fil Maj

src/api-proxy.ts

@@ -1,6 +1,8 @@
 import { BaseSlackAPIClient } from "./base-client.ts";
 import { BaseResponse, SlackAPIClient, SlackAPIMethodArgs } from "./types.ts";
 
+const DO_NOT_PROXY = ["then"];
+
 type APICallback = {
   (method: string, payload?: SlackAPIMethodArgs): Promise<BaseResponse>;
 };
@@ -46,7 +48,10 @@ export const APIProxy = (
   const proxy = new Proxy(objectToProxy, {
     get(obj, prop) {
       // We're attempting to access a property that doesn't exist, so create a new nested proxy
-      if (typeof prop === "string" && !(prop in obj)) {
+      if (
+        typeof prop === "string" && !DO_NOT_PROXY.includes(prop) &&
+        !(prop in obj)
+      ) {
         return APIProxy(null, apiCallback, ...path, prop);
       }
 

src/api-proxy_test.ts

@@ -3,30 +3,57 @@ import { BaseSlackAPIClient } from "./base-client.ts";
 import { SlackAPIMethodArgs } from "./types.ts";
 import { assertSpyCall, spy } from "./dev_deps.ts";
 
-Deno.test("APIProxy", async () => {
+Deno.test("APIProxy", async (t) => {
   const baseClient = new BaseSlackAPIClient("test-token");
-  const clientToProxy = {
-    apiCall: baseClient.apiCall.bind(baseClient),
-    response: baseClient.response.bind(baseClient),
-  };
+  const generateClientProxy = (client: BaseSlackAPIClient) => ({
+    apiCall: client.apiCall.bind(client),
+    response: client.response.bind(client),
+  });
+
+  await t.step("should proxy legit Slack API calls", async () => {
+    const clientToProxy = generateClientProxy(baseClient);
+
+    const apiCallHandler = (_method: string, _payload?: SlackAPIMethodArgs) => {
+      return Promise.resolve({
+        ok: true,
+        toFetchResponse: () => new Response(),
+      });
+    };
+    const apiCallHandlerSpy = spy(apiCallHandler);
 
-  const apiCallHandler = (_method: string, _payload?: SlackAPIMethodArgs) => {
-    return Promise.resolve({ ok: true, toFetchResponse: () => new Response() });
-  };
-  const apiCallHandlerSpy = spy(apiCallHandler);
+    const client = APIProxy(clientToProxy, apiCallHandlerSpy);
 
-  const client = APIProxy(clientToProxy, apiCallHandlerSpy);
+    const payload = { text: "proxied call", channel: "" };
+    await client.chat.postMessage(payload);
 
-  const payload = { text: "proxied call", channel: "" };
-  await client.chat.postMessage(payload);
+    assertSpyCall(apiCallHandlerSpy, 0, {
+      args: ["chat.postMessage", payload],
+    });
 
-  assertSpyCall(apiCallHandlerSpy, 0, {
-    args: ["chat.postMessage", payload],
+    await client.admin.apps.approved.list();
+
+    assertSpyCall(apiCallHandlerSpy, 1, {
+      args: ["admin.apps.approved.list", undefined],
+    });
   });
 
-  await client.admin.apps.approved.list();
+  await t.step("should not proxy Promise methods like `then`", () => {
+    const clientToProxy = generateClientProxy(baseClient);
+
+    const apiCallHandler = (_method: string, _payload?: SlackAPIMethodArgs) => {
+      return Promise.resolve({
+        ok: true,
+        toFetchResponse: () => new Response(),
+      });
+    };
+    const apiCallHandlerSpy = spy(apiCallHandler);
+
+    const client = APIProxy(clientToProxy, apiCallHandlerSpy);
 
-  assertSpyCall(apiCallHandlerSpy, 1, {
-    args: ["admin.apps.approved.list", undefined],
+    // re: https://github.com/slackapi/deno-slack-api/issues/107
+    // @ts-expect-error client does not have `then` but thenable feature detection at runtime may invoke or test for the method
+    if (client.then) {
+      throw new Error("APIProxy should have no `then`!");
+    }
   });
 });