fix: $close to set original error in .cause (#25)

AriPerkkio · web-flow · commit 40ee074dad5a · 2025-07-13T10:36:56.000+02:00
diff --git a/src/index.ts b/src/index.ts
@@ -269,10 +269,17 @@ export function createBirpc<RemoteFunctions = Record<string, never>, LocalFuncti
     },
   }) as BirpcReturn<RemoteFunctions, LocalFunctions>
 
-  function close(error?: Error) {
+  function close(customError?: Error) {
     closed = true
     rpcPromiseMap.forEach(({ reject, method }) => {
-      reject(error || new Error(`[birpc] rpc is closed, cannot call "${method}"`))
+      const error = new Error(`[birpc] rpc is closed, cannot call "${method}"`)
+
+      if (customError) {
+        customError.cause ??= error
+        return reject(customError)
+      }
+
+      reject(error)
     })
     rpcPromiseMap.clear()
     off(onMessage)
diff --git a/test/close.test.ts b/test/close.test.ts
@@ -25,7 +25,7 @@ it('stops the rpc promises', async () => {
 })
 
 it('stops the rpc promises with a custom message', async () => {
-  expect.assertions(1)
+  expect.assertions(2)
   const rpc = createBirpc<{ hello: () => string }>({}, {
     on() {},
     post() {},
@@ -37,10 +37,39 @@ it('stops the rpc promises with a custom message', async () => {
     (err) => {
       // Promise should reject
       expect(err.message).toBe('Custom error')
+
+      // Original error should be present
+      expect(err.cause.message).toBe('[birpc] rpc is closed, cannot call "hello"')
     },
   )
   nextTick(() => {
     rpc.$close(new Error('Custom error'))
   })
   await promise
 })
+
+it('custom error\'s cause is not overwritten', async () => {
+  expect.assertions(2)
+  const rpc = createBirpc<{ hello: () => string }>({}, {
+    on() {},
+    post() {},
+  })
+  const promise = rpc.hello().then(
+    () => {
+      throw new Error('Promise should not resolve')
+    },
+    (err) => {
+      // Promise should reject
+      expect(err.message).toBe('Custom error')
+
+      // Custom error cause should be present
+      expect(err.cause.message).toBe('Custom cause')
+    },
+  )
+  nextTick(() => {
+    const error = new Error('Custom error')
+    error.cause = new Error('Custom cause')
+    rpc.$close(error)
+  })
+  await promise
+})
