chore: allow evaluating Error objects (#31691)

Previously, Error objects were replaced with strings.
Now, Error objects are reconstructed back from the serialized value.

packages/playwright-core/src/protocol/serializers.ts

@@ -49,6 +49,12 @@ function innerParseSerializedValue(value: SerializedValue, handles: any[] | unde
     return new URL(value.u);
   if (value.bi !== undefined)
     return BigInt(value.bi);
+  if (value.e !== undefined) {
+    const error = new Error(value.e.m);
+    error.name = value.e.n;
+    error.stack = value.e.s;
+    return error;
+  }
   if (value.r !== undefined)
     return new RegExp(value.r.p, value.r.f);
 
@@ -113,14 +119,8 @@ function innerSerializeValue(value: any, handleSerializer: (value: any) => Handl
     return { s: value };
   if (typeof value === 'bigint')
     return { bi: value.toString() };
-  if (isError(value)) {
+  if (isError(value))
-    const error = value;
+    return { e: { n: value.name, m: value.message, s: value.stack || '' } };
-    if ('captureStackTrace' in globalThis.Error) {
-      // v8
-      return { s: error.stack || '' };
-    }
-    return { s: `${error.name}: ${error.message}\n${error.stack}` };
-  }
   if (isDate(value))
     return { d: value.toJSON() };
   if (isURL(value))

packages/playwright-core/src/protocol/validator.ts

@@ -58,6 +58,11 @@ scheme.SerializedValue = tObject({
   d: tOptional(tString),
   u: tOptional(tString),
   bi: tOptional(tString),
+  e: tOptional(tObject({
+    m: tString,
+    n: tString,
+    s: tString,
+  })),
   r: tOptional(tObject({
     p: tString,
     f: tString,

packages/playwright-core/src/server/isomorphic/utilityScriptSerializers.ts

@@ -20,7 +20,8 @@ export type SerializedValue =
     { d: string } |
     { u: string } |
     { bi: string } |
-    { r: { p: string, f: string} } |
+    { e: { n: string, m: string, s: string } } |
+    { r: { p: string, f: string } } |
     { a: SerializedValue[], id: number } |
     { o: { k: string, v: SerializedValue }[], id: number } |
     { ref: number } |
@@ -94,6 +95,12 @@ export function source() {
         return new URL(value.u);
       if ('bi' in value)
         return BigInt(value.bi);
+      if ('e' in value) {
+        const error = new Error(value.e.m);
+        error.name = value.e.n;
+        error.stack = value.e.s;
+        return error;
+      }
       if ('r' in value)
         return new RegExp(value.r.p, value.r.f);
       if ('a' in value) {
@@ -163,14 +170,8 @@ export function source() {
     if (typeof value === 'bigint')
       return { bi: value.toString() };
 
-    if (isError(value)) {
+    if (isError(value))
-      const error = value;
+      return { e: { n: value.name, m: value.message, s: value.stack || '' } };
-      if (error.stack?.startsWith(error.name + ': ' + error.message)) {
-        // v8
-        return error.stack;
-      }
-      return `${error.name}: ${error.message}\n${error.stack}`;
-    }
     if (isDate(value))
       return { d: value.toJSON() };
     if (isURL(value))

packages/protocol/src/channels.ts

@@ -177,6 +177,11 @@ export type SerializedValue = {
   d?: string,
   u?: string,
   bi?: string,
+  e?: {
+    m: string,
+    n: string,
+    s: string,
+  },
   r?: {
     p: string,
     f: string,

packages/protocol/src/protocol.yml

@@ -82,6 +82,13 @@ SerializedValue:
     u: string?
     # String representation of BigInt.
     bi: string?
+    # Serialized Error object.
+    e:
+      type: object?
+      properties:
+        m: string
+        n: string
+        s: string
     # Regular expression pattern and flags.
     r:
       type: object?

tests/page/page-evaluate.spec.ts

@@ -585,13 +585,37 @@ it('should evaluate exception with a function on the stack', async ({ page }) =>
       return new Error('error message');
     })();
   });
-  expect(error).toContain('Error: error message');
+  expect(error.message).toBe('error message');
-  expect(error).toContain('functionOnStack');
+  expect(error.stack).toContain('functionOnStack');
 });
 
 it('should evaluate exception', async ({ page }) => {
-  const error = await page.evaluate(`new Error('error message')`);
+  const error = await page.evaluate(() => {
-  expect(error).toContain('Error: error message');
+    function innerFunction() {
+      const e = new Error('error message');
+      e.name = 'foobar';
+      return e;
+    }
+    return innerFunction();
+  });
+  expect(error).toBeInstanceOf(Error);
+  expect((error as Error).message).toBe('error message');
+  expect((error as Error).name).toBe('foobar');
+  expect((error as Error).stack).toContain('innerFunction');
+});
+
+it('should pass exception argument', async ({ page }) => {
+  function innerFunction() {
+    const e = new Error('error message');
+    e.name = 'foobar';
+    return e;
+  }
+  const received = await page.evaluate(e => {
+    return { message: e.message, name: e.name, stack: e.stack };
+  }, innerFunction());
+  expect(received.message).toBe('error message');
+  expect(received.name).toBe('foobar');
+  expect(received.stack).toContain('innerFunction');
 });
 
 it('should evaluate date', async ({ page }) => {