From 911d2d22de2fda78c103fc2a0d552c88b78d3aba Mon Sep 17 00:00:00 2001
From: Felix Becker <felix.b@outlook.com>
Date: Sat, 25 Apr 2020 15:23:34 +0200
Subject: [PATCH 1/2] Add failing test for throwing scalars

---
 tests/same_window.comlink.test.js | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tests/same_window.comlink.test.js b/tests/same_window.comlink.test.js
index 7bfb9aa7..e64838f2 100644
--- a/tests/same_window.comlink.test.js
+++ b/tests/same_window.comlink.test.js
@@ -147,6 +147,21 @@ describe("Comlink in the same realm", function() {
     }
   });
 
+  it("can rethrow scalars", async function() {
+    const thing = Comlink.wrap(this.port1);
+    Comlink.expose(_ => {
+      throw "oops";
+    }, this.port2);
+    try {
+      await thing();
+      throw "Should have thrown";
+    } catch (err) {
+      expect(err).to.not.eq("Should have thrown");
+      expect(err).to.be("oops");
+      expect(typeof err).to.be("string");
+    }
+  });
+
   it("can work with parameterized functions", async function() {
     const thing = Comlink.wrap(this.port1);
     Comlink.expose((a, b) => a + b, this.port2);

From a88f6002985720de265a4b9869e69c88f53fec20 Mon Sep 17 00:00:00 2001
From: Surma <surma@surma.link>
Date: Mon, 27 Apr 2020 17:01:45 +0100
Subject: [PATCH 2/2] Switch to throw marker to allow throwing scalars

---
 src/comlink.ts                    | 35 ++++++++++++++-----------------
 tests/same_window.comlink.test.js |  8 +++----
 2 files changed, 20 insertions(+), 23 deletions(-)

diff --git a/src/comlink.ts b/src/comlink.ts
index b734ff5e..3cc4e90d 100644
--- a/src/comlink.ts
+++ b/src/comlink.ts
@@ -25,7 +25,7 @@ export { Endpoint };
 export const proxyMarker = Symbol("Comlink.proxy");
 export const createEndpoint = Symbol("Comlink.endpoint");
 export const releaseProxy = Symbol("Comlink.releaseProxy");
-const throwSet = new WeakSet();
+const throwMarker = Symbol("Comlink.thrown");
 
 // prettier-ignore
 type Promisify<T> =
@@ -100,24 +100,23 @@ export const transferHandlers = new Map<string, TransferHandler>([
   [
     "throw",
     {
-      canHandle: obj => throwSet.has(obj),
-      serialize(obj) {
-        const isError = obj instanceof Error;
-        let serialized = obj;
+      canHandle: obj => typeof obj === "object" && throwMarker in obj,
+      serialize({ value }) {
+        const isError = value instanceof Error;
+        let serialized = { isError, value };
         if (isError) {
-          serialized = {
-            isError,
-            message: obj.message,
-            stack: obj.stack
+          serialized.value = {
+            message: value.message,
+            stack: value.stack
           };
         }
         return [serialized, []];
       },
-      deserialize(obj) {
-        if ((obj as any).isError) {
-          throw Object.assign(new Error(), obj);
+      deserialize(serialized) {
+        if (serialized.isError) {
+          throw Object.assign(new Error(), serialized.value);
         }
-        throw obj;
+        throw serialized.value;
       }
     }
   ]
@@ -173,14 +172,12 @@ export function expose(obj: any, ep: Endpoint = self as any) {
           }
           break;
       }
-    } catch (e) {
-      returnValue = e;
-      throwSet.add(e);
+    } catch (value) {
+      returnValue = { value, [throwMarker]: 0 };
     }
     Promise.resolve(returnValue)
-      .catch(e => {
-        throwSet.add(e);
-        return e;
+      .catch(value => {
+        return { value, [throwMarker]: 0 };
       })
       .then(returnValue => {
         const [wireValue, transferables] = toWireValue(returnValue);
diff --git a/tests/same_window.comlink.test.js b/tests/same_window.comlink.test.js
index e64838f2..be93cc3a 100644
--- a/tests/same_window.comlink.test.js
+++ b/tests/same_window.comlink.test.js
@@ -142,7 +142,7 @@ describe("Comlink in the same realm", function() {
       await thing();
       throw "Should have thrown";
     } catch (err) {
-      expect(err).to.not.eq("Should have thrown");
+      expect(err).to.not.equal("Should have thrown");
       expect(err.test).to.equal(true);
     }
   });
@@ -156,9 +156,9 @@ describe("Comlink in the same realm", function() {
       await thing();
       throw "Should have thrown";
     } catch (err) {
-      expect(err).to.not.eq("Should have thrown");
-      expect(err).to.be("oops");
-      expect(typeof err).to.be("string");
+      expect(err).to.not.equal("Should have thrown");
+      expect(err).to.equal("oops");
+      expect(typeof err).to.equal("string");
     }
   });